Showing papers in "Journal of Chemical Physics in 2002"
TL;DR: The polarizable continuum model (PCM) as discussed by the authors was used for the calculation of molecular energies, structures, and properties in liquid solution, in order to extend its range of applications and to improve its accuracy.
Abstract: The polarizable continuum model (PCM), used for the calculation of molecular energies, structures, and properties in liquid solution has been deeply revised, in order to extend its range of applications and to improve its accuracy. The main changes effect the definition of solute cavities, of solvation charges and of the PCM operator added to the molecular Hamiltonian, as well as the calculation of energy gradients, to be used in geometry optimizations. The procedure can be equally applied to quantum mechanical and to classical calculations; as shown also with a number of numerical tests, this PCM formulation is very efficient and reliable. It can also be applied to very large solutes, since all the bottlenecks have been eliminated to obtain a procedure whose time and memory requirements scale linearly with solute size. The present procedure can be used to compute solvent effects at a number of different levels of theory on almost all the chemical systems which can be studied in vacuo.
2,190 citations
TL;DR: In this paper, the authors present theory, implementation, and validation of excited state properties obtained from time-dependent density functional theory (TDDFT), based on a fully variational expression for the excited state energy, a compact derivation of first order properties is given.
Abstract: This work presents theory, implementation, and validation of excited state properties obtained from time-dependent density functional theory (TDDFT). Based on a fully variational expression for the excited state energy, a compact derivation of first order properties is given. We report an implementation of analytic excited state gradients and charge moments for local, gradient corrected, and hybrid functionals, as well as for the configuration interaction singles (CIS) and time-dependent Hartree–Fock (TDHF) methods. By exploiting analogies to ground state energy and gradient calculations, efficient techniques can be transferred to excited state methods. Benchmark results demonstrate that, for low-lying excited states, geometry optimizations are not substantially more expensive than for the ground state, independent of the molecular size. We assess the quality of calculated adiabatic excitation energies, structures, dipole moments, and vibrational frequencies by comparison with accurate experimental data for a variety of excited states and molecules. Similar trends are observed for adiabatic excitation energies as for vertical ones. TDDFT is more robust than CIS and TDHF, in particular, for geometries differing significantly from the ground state minimum. The TDDFT excited state structures, dipole moments, and vibrational frequencies are of a remarkably high quality, which is comparable to that obtained in ground state density functional calculations. Thus, yielding considerably more accurate results at similar computational cost, TDDFT rivals CIS as a standard method for calculating excited state properties in larger molecules.
1,976 citations
TL;DR: In this paper, a quantum dissipation theory is constructed with the system-bath interaction being treated rigorously at the second-order cumulant level for both reduced dynamics and initial canonical boundary condition.
Abstract: A quantum dissipation theory is constructed with the system–bath interaction being treated rigorously at the second-order cumulant level for both reduced dynamics and initial canonical boundary condition. The theory is valid for arbitrary bath correlation functions and time-dependent external driving fields, and satisfies correlated detailed-balance relation at any temperatures. The general formulation assumes a particularly simple form in driven Brownian oscillator systems in which the correlated driving-dissipation effects can be accounted for exactly in terms of local-field correction. Remarks on a class of widely used phenomenological quantum master equations that neglects the bath dispersion-induced dissipation are also made in contact with the present theory.
1,731 citations
TL;DR: In this paper, the effect of size and shape on the spectral response of individual silver nanoparticles was studied and it was shown that specific geometrical shapes give distinct spectral responses.
Abstract: We present a systematic study of the effect of size and shape on the spectral response of individual silver nanoparticles. An experimental method has been developed that begins with the detection and characterization of isolated nanoparticles in the optical far field. The plasmon resonance optical spectrum of many individual nanoparticles are then correlated to their size and shape using high-resolution transmission electron microscopy. We find that specific geometrical shapes give distinct spectral responses. In addition, inducing subtle changes in the particles’ morphology by heating causes a shift in the individual particle spectrum and provides a simple means of tuning the spectral response to a desired optical wavelength. Improved colloidal preparation methods could potentially lead to homogeneous populations of identical particle shapes and colors. These multicolor colloids could be used as biological labels, surface enhanced Raman scattering substrates, or near field optical microscopy sources cove...
1,687 citations
TL;DR: In this article, the second-order Moller-Plesset perturbation theory (MP2) correlation energy with the cardinal number X is investigated for the correlation consistent basis-set series cc-pVXZ and cc-PV(X+d)Z.
Abstract: The convergence of the second-order Moller–Plesset perturbation theory (MP2) correlation energy with the cardinal number X is investigated for the correlation consistent basis-set series cc-pVXZ and cc-pV(X+d)Z. For the aug-cc-pVXZ and aug-cc-pV(X+d)Z series the convergence of the MP2 correlation contribution to the dipole moment is studied. It is found that, when d-shell electrons cannot be frozen, the cc-pVXZ and aug-cc-pVXZ basis sets converge much slower for third-row elements then they do for first- and second-row elements. Based on the results of these studies criteria are deduced for the accuracy of auxiliary basis sets used in the resolution of the identity (RI) approximation for electron repulsion integrals. Optimized auxiliary basis sets for RI-MP2 calculations fulfilling these criteria are reported for the sets cc-pVXZ, cc-pV(X+d)Z, aug-cc-pVXZ, and aug-cc-pV(X+d)Z with X=D, T, and Q. For all basis sets the RI error in the MP2 correlation energy is more than two orders of magnitude smaller than...
1,660 citations
TL;DR: In this article, two different optimization strategies were investigated, which led to two families of core-valence basis sets when the optimized functions were added to the standard correlation consistent basis sets (cc-pVnZ).
Abstract: Correlation consistent basis sets for accurately describing core–core and core–valence correlation effects in atoms and molecules have been developed for the second row atoms Al–Ar. Two different optimization strategies were investigated, which led to two families of core–valence basis sets when the optimized functions were added to the standard correlation consistent basis sets (cc-pVnZ). In the first case, the exponents of the augmenting primitive Gaussian functions were optimized with respect to the difference between all-electron and valence–electron correlated calculations, i.e., for the core–core plus core–valence correlation energy. This yielded the cc-pCVnZ family of basis sets, which are analogous to the sets developed previously for the first row atoms [D. E. Woon and T. H. Dunning, Jr., J. Chem. Phys. 103, 4572 (1995)]. Although the cc-pCVnZ sets exhibit systematic convergence to the all-electron correlation energy at the complete basis set limit, the intershell (core–valence) correlation energ...
1,618 citations
TL;DR: In this paper, the topological and energetic properties of the electron density distribution ρ(r) of isolated pairwise H⋯F interaction have been theoretically calculated at several geometries and represented against the corresponding internuclear distances.
Abstract: The topological and energetic properties of the electron density distribution ρ(r) of the isolated pairwise H⋯F interaction have been theoretically calculated at several geometries (0.8
1,395 citations
TL;DR: In this article, the n-electron valence state perturbation theory is reformulated in a spin-free formalism, concentrating on the "strongly contracted" and "partially contracted" variants.
Abstract: The n-electron valence state perturbation theory is reformulated in a spin-free formalism, concentrating on the “strongly contracted” and “partially contracted” variants. The new formulation is based on the introduction of average values in the unperturbed state of excitation operators which bear resemblance with analogous ones occurring in the extended Koopmans’ theorem and in the equations-of-motion technique. Such auxiliary quantities, which allow the second-order perturbation contribution to the energy to be evaluated very efficiently, can be calculated at the outset provided the unperturbed four-particle spinless density matrix in the active orbital space is available. A noticeable inequality concerning second-order energy contributions of the same type between the strongly and partially contracted versions is proven to hold. An example concerning the successful calculation of the potential energy curve for the Cr2 molecule is discussed.
882 citations
TL;DR: In this paper, an empirical method has been designed to account for van der Waals interactions in practical molecular calculations with density functional theory, which adds to the density functional electronic structure calculations an additional attraction energy EvdW=−fd(R)C6R−6.
Abstract: An empirical method has been designed to account for the van der Waals interactions in practical molecular calculations with density functional theory. For each atom pair separated at a distance R, the method adds to the density functional electronic structure calculations an additional attraction energy EvdW=−fd(R)C6R−6, where fd(R) is the damping function which equals to one at large value of R and zero at small value of R. The coefficients C6 for pair interactions between hydrogen, carbon, nitrogen, and oxygen atoms have been developed in this work by a least-square fitting to the molecular C6 coefficients obtained from the dipole oscillator strength distribution method by Meath and co-workers. Two forms of the damping functions have been studied, with one dropping to zero at short distances much faster than the other. Four density functionals have been examined: Becke’s three parameter hybrid functional with the Lee-Yang-Parr correlation functional, Becke’s 1988 exchange functional with the LYP correl...
769 citations
TL;DR: Two variants of the Hamiltonian replica exchange methods (REMs) for efficient configuration sampling are developed, including the scaled hydrophobicity REM and the phantom chain REM, and their performance is compared with the ordinary REM.
Abstract: Motivated by the protein structure prediction problem, we develop two variants of the Hamiltonian replica exchange methods (REMs) for efficient configuration sampling, (1) the scaled hydrophobicity REM and (2) the phantom chain REM, and compare their performance with the ordinary REM. We first point out that the ordinary REM has a shortage for the application to large systems such as biomolecules and that the Hamiltonian REM, an alternative formulation of the REM, can give a remedy for it. We then propose two examples of the Hamiltonian REM that are suitable for a coarse-grained protein model. (1) The scaled hydrophobicity REM prepares replicas that are characterized by various strengths of hydrophobic interaction. The strongest interaction that mimics aqueous solution environment makes proteins folding, while weakened hydrophobicity unfolds proteins as in organic solvent. Exchange between these environments enables proteins to escape from misfolded traps and accelerate conformational search. This resembl...
720 citations
TL;DR: In this paper, the applicability, accuracy and efficiency of this method were compared with two equilibrium methods and another nonequilibrium method, using simulations of a Lennard-Jones fluid and the SPC and SPC/E [(extended) simple point charge] water models.
Abstract: Several methods are available for calculating shear viscosities of liquids from molecular dynamics simulations. There are equilibrium methods based on pressure or momentum fluctuations and several nonequilibrium methods. For the nonequilibrium method using a periodic shear flow, all relevant quantities, including the accuracy, can be estimated before performing the simulation. We compared the applicability, accuracy and efficiency of this method with two equilibrium methods and another nonequilibrium method, using simulations of a Lennard-Jones fluid and the SPC and SPC/E [(extended) simple point charge] water models.
TL;DR: This paper addresses one aspect of this problem: the case in which reacting species fluctuate by different orders of magnitude, and provides a theoretical background for such approximations and outlines strategies for computing these approximation.
Abstract: Exact methods are available for the simulation of isothermal, well-mixed stochastic chemical kinetics. As increasingly complex physical systems are modeled, however, these methods become difficult to solve because the computational burden scales with the number of reaction events. This paper addresses one aspect of this problem: the case in which reacting species fluctuate by different orders of magnitude. By partitioning the system into subsets of “fast” and “slow” reactions, it is possible to bound the computational load by approximating “fast” reactions either deterministically or as Langevin equations. This paper provides a theoretical background for such approximations and outlines strategies for computing these approximations. Two motivating examples drawn from the fields of particle technology and biotechnology illustrate the accuracy and computational efficiency of these approximations.
TL;DR: In this paper, the authors reformulate Rosenfeld's fundamental measure theory using the excess Helmholtz energy density from the Boublik-Mansoori-Carnahan-Starling-Leland equation of state instead of that from the scaled-particle theory.
Abstract: We reformulate Rosenfeld’s fundamental-measure theory using the excess Helmholtz energy density from the Boublik–Mansoori–Carnahan–Starling–Leland equation of state instead of that from the scaled-particle theory. The new density functional theory yields improved density distributions, especially the contact densities, of inhomogeneous hard-sphere fluids as well as more accurate direct and pair correlation functions of homogeneous hard spheres including those of highly asymmetric mixtures. This new density functional theory will provide an accurate reference for the further development of a statistical-thermodynamic theory of complex fluids at uniform and at inhomogeneous conditions.
TL;DR: The most general parametrization of the unitary matrices in the Douglas-Kroll (DK) transformation sequence for relativistic electronic structure calculations was derived in this article.
Abstract: We derive the most general parametrization of the unitary matrices in the Douglas–Kroll (DK) transformation sequence for relativistic electronic structure calculations. It is applied for a detailed analysis of the generalized DK transformation up to fifth order in the external potential. While DKH2–DKH4 are independent of the parametrization of the unitary matrices, DKH5 turns out to be dependent on the third expansion coefficient of the innermost unitary transformation which is carried out after the initial free-particle Foldy–Wouthuysen transformation. The freedom in the choice of this expansion coefficient vanishes consistently if the optimum unitary transformation is sought for. Since the standard protocol of the DK method is the application of unitary transformations to the one-electron Dirac operator, we analyze the DKH procedure up to fifth order for hydrogenlike atoms. We find remarkable accuracy of the higher-order DK corrections as compared to the exact Dirac ground state energy. In the case of ...
TL;DR: In this article, a fully Hamiltonian and computationally efficient scheme to include the electrostatic effects due to the classical environment in a Car-Parrinello mixed quantum mechanics/molecular mechanics (QM/MM) method is presented.
Abstract: We present a fully Hamiltonian and computationally efficient scheme to include the electrostatic effects due to the classical environment in a Car–Parrinello mixed quantum Mechanics/molecular mechanics (QM/MM) method. The polarization due to the MM atoms close to the quantum system is described by a Coulombic potential modified at short range. We show that the functional form of this potential has to be chosen carefully in order to obtain the correct interaction properties and to prevent an unphysical escape of the electronic density to the MM atoms (the so-called spill-out effect). The interaction between the QM system and the more distant MM atoms is modeled by a Hamiltonian term explicitly coupling the multipole moments of the quantum charge distribution with the classical point charges. Our approach remedies some of the well known deficiencies of current electrostatic coupling schemes in QM/MM methods, allowing molecular dynamics simulations of mixed systems within a fully consistent and energy conser...
TL;DR: The scanning tunneling microscope (STM) as discussed by the authors is a state-of-the-art system for direct visualization of chemistry by revealing the fundamental properties of atoms and molecules and their interactions with each other and the environment.
Abstract: The ability to probe individual atoms and molecules have made it possible to reveal properties which otherwise would be hidden in the study of an ensemble of atoms and molecules. The scanning tunneling microscope (STM) with its unmatched spatial resolution and versatility literally allows us to touch atoms and molecules one at a time and to carry out experiments which previously were only imagined. One of the great attributes of the STM is that it provides a real space view of the individual molecules and the atomic landscape of their environment, thus removing many of the uncertainties surrounding the nature of the system under study. Combining its imaging, manipulation, spectroscopic characterization, and chemical modification capabilities, the STM has enabled direct visualization of chemistry by revealing the fundamental properties of atoms and molecules and their interactions with each other and the environment. While femtosecond lasers have made it possible to study chemistry at the temporal limit, the STM provides an understanding of chemistry at the spatial limit.
TL;DR: In this paper, a density matrix renormalization group (DMRG) algorithm was proposed for quantum chemistry problems, such as the water molecule, the twisting barrier of ethene, and the dissociation of nitrogen.
Abstract: We study the recently developed Density Matrix Renormalization Group (DMRG) algorithm in the context of quantum chemistry In contrast to traditional approaches, this algorithm is believed to yield arbitrarily high accuracy in the energy with only polynomial computational effort We describe in some detail how this is achieved We begin by introducing the principles of the renormalization procedure, and how one formulates an algorithm for use in quantum chemistry The renormalization group algorithm is then interpreted in terms of familiar quantum chemical concepts, and its numerical behavior, including its convergence and computational cost, are studied using both model and real systems The asymptotic convergence of the algorithm is derived Finally, we examine the performance of the DMRG on widely studied chemical problems, such as the water molecule, the twisting barrier of ethene, and the dissociation of nitrogen In all cases, the results compare favorably with the best existing quantum chemical methods, and particularly so when the nondynamical correlation is strong Some perspectives for future development are given
TL;DR: In this article, the exact exchange part in hybrid density functionals is analyzed with respect to the prediction of ground state multiplicities, and it is shown that the energy splitting of high-spin and low-spin states of Fe-sulfur complexes is linearly dependent on exact exchange.
Abstract: The exact exchange part in hybrid density functionals is analyzed with respect to the prediction of ground state multiplicities. It has been found [M. Reiher, O. Salomon, and B. A. Hess, Theor. Chem. Acc., 107, 48 (2001)] that pure and hybrid density functionals yield energy splittings between high-spin and low-spin states of Fe–sulfur complexes that differ by more than 100 kJ/mol and thus fail to reliably predict the correct multiplicity of the ground state. This deviation can lead to meaningless reaction energetics for metal-catalyzed reactions. The finding that the energy splitting depends linearly on the exact exchange admixture parameter led to a new parametrization of the B3LYP functional which was dubbed B3LYP⋆. In the present paper we investigate the generality and transferability of this functional. We study the extent to which the exact exchange admixture affects the thermochemistry validated with respect to the reference data set of molecules from the G2 test set. Metallocenes and bis(benzene) metal complexes of the first transition metal period are chosen to test the transferability of the findings for Fe–sulfur complexes. Moreover, the slope of the linear dependence of the energy splitting of high-spin and low-spin states on the amount of admixture of exact exchange is studied in detail.
TL;DR: In this article, a combined experimental and theoretical study of small gold cluster anions is performed, where the experimental effort consists of ion mobility measurements that lead to the assignment of the collision cross sections for the different cluster sizes at room temperature and the theoretical study is based on abomolecular dynamics calculations with the goal to find energetically favorable candidate structures.
Abstract: A combined experimental and theoretical study of small gold cluster anions is performed. The experimental effort consists of ion mobilitymeasurements that lead to the assignment of the collision cross sections for the different cluster sizes at room temperature. The theoretical study is based on ab initiomolecular dynamics calculations with the goal to find energetically favorable candidate structures. By comparison of the theoretical results with the measured collision cross sections as well as vertical detachment energies (VDEs) from the literature, we assign structures for the small Au n − ions (n<13) and locate the transition from planar to three-dimensional structures. While a unique assignment based on the observed VDEs alone is generally not possible, the collision cross sections provide a direct and rather sensitive measure of the cluster structure. In contrast to what was expected from other metal clusters and previous theoretical studies, the structural transition occurs at an unusually large cluster size of twelve atoms.
TL;DR: Theoretical analysis and results of calculations are put forward to interpret the energies −ek of the occupied Kohn-Sham (KS) orbitals as approximate but rather accurate relaxed vertical ionization potentials (VIPs) Ik as discussed by the authors.
Abstract: Theoretical analysis and results of calculations are put forward to interpret the energies −ek of the occupied Kohn–Sham (KS) orbitals as approximate but rather accurate relaxed vertical ionization potentials (VIPs) Ik. Exact relations between ek and Ik are established with a set of linear equations for the ek, which are expressed through Ik and the matrix elements ekresp of a component of the KS exchange-correlation (xc) potential vxc, the response potential vresp. Although −Ik will be a leading contribution to ek, other Ij≠k do enter through coupling terms which are determined by the overlaps between the densities of the KS orbitals as well as by overlaps between the KS and Dyson orbital densities. The orbital energies obtained with “exact” KS potentials are compared with the experimental VIPs of the molecules N2, CO, HF, and H2O. Very good agreement between the accurate −ek of the outer valence KS orbitals and the corresponding VIPs is established. The average difference, approaching 0.1 eV, is about a...
TL;DR: In this paper, the authors performed ion mobility measurements on gold cluster cations generated by pulsed laser vaporization and found that they have planar structures for n = 3-7.
Abstract: We have performed ion mobility measurements on gold cluster cations Aun+ generated by pulsed laser vaporization. For clusters with n<14, experimental cross sections are compared with theoretical results from density functional calculations. This comparison allows structural assignment. We find that room temperature gold cluster cations have planar structures for n=3–7. Starting at n=8 they form three dimensional structures with (slightly distorted) fragments of the bulk phase structure being observed for n=8–10.
TL;DR: The generalized Born (GB) model is a simple continuum dielectric model for the calculation of molecular electrostatic solvation energies as mentioned in this paper, which is a pairwise approximation to the solution of the Poisson equation for continuum electrostatic Solvation.
Abstract: The generalized Born (GB) model is a simple continuum dielectric model for the calculation of molecular electrostatic solvation energies. It is a pairwise approximation to the solution of the Poisson equation for continuum electrostatic solvation. Key to the GB method is the calculation of Born radii for every atom in the system. We introduce two new methods for determining Born radii. The first is a two-parameter grid-based method that uses nearly the same molecular volume that is used in conventional Poisson calculations. The second is a five-parameter analytical method that utilizes a molecular volume built from a superposition of atomic functions. The analytical method, distinct from the grid-based algorithm, is amenable to force-based calculations, e.g., energy minimization and molecular dynamics. Unlike other Born radii methods, both algorithms employ a new empirically determined correction term that includes energetic effects beyond the Coulomb field approximation. With this correction term, the grid-based algorithm generally yields Born radii with greater than 0.99 correlation versus converged numerically derived Poisson Born radii. The analytical method reproduces Born radii with approximately 0.95 correlation versus Poisson-derived Born radii. With respect to absolute solvation energies, the grid-based method achieves an overall 1.3% error versus converged Poisson solutions for a set of 3029 single-chain proteins obtained from the Brookhaven Protein Data Bank. On the other hand, the analytic method delivers modest 2–4 % errors versus the Poisson solutions for the same data set. Results concerning absolute solvation energies of RNA and relative solvation energies in two sets of protein conformations are also presented.
TL;DR: In this article, the kinetic energy density Tau variable was introduced to enhance the performance of previous functionals, leading to highly accurate functionals with and without the use of exact exchange.
Abstract: New density functionals, using the kinetic-energy density Tau are reported. The newly introduced variable enhances the performance of previous functionals, leading to highly accurate functionals with and without the use of exact exchange. All these functionals are compared to commonly used functionals for a large test set, looking also at reactions and hydrogen bonded systems. Furthermore, their physical plausibility is discussed.
TL;DR: In this article, the crossover sizes among structural motifs are directly calculated, considering cluster up to sizes N≃40 000, for all the systems considered, it is found that icosahedra are favored at small sizes, decahedra at intermediate sizes, and truncated octahedral at large sizes.
Abstract: The energetics of nanoclusters is investigated for five different metals (Ag, Cu, Au, Pd, and Pt) by means of quenched molecular dynamics simulations. Results are obtained for two different semiempirical potentials. Three different structural motifs are considered: icosahedra (Ih), decahedra (Dh), and truncated octahedra (TO). The crossover sizes among structural motifs are directly calculated, considering cluster up to sizes N≃40 000. For all the systems considered, it is found that icosahedra are favored at small sizes, decahedra at intermediate sizes, and truncated octahedra at large sizes. However, the crossover sizes depend strongly on the metal: in Cu, the icosahedral interval is rather large, and it is followed by a very wide decahedral window; on the contrary, in Au, the icosahedral interval is practically absent, and the decahedral window is narrow. The other metals display intermediate behaviors, Ag being close to Cu, and Pd and Pt being close to Au. A simple criterion, which is based on the rat...
TL;DR: In this article, an extended Lagrangian is used to propagate the density matrix in a basis of atom centered Gaussian functions, and the results of trajectory calculations obtained by this method are compared with the Born-Oppenheimer approach (BO), in which the density is converged at each step rather than propagated.
Abstract: In a recently developed approach to ab initio molecular dynamics (ADMP), we used an extended Lagrangian to propagate the density matrix in a basis of atom centered Gaussian functions. Results of trajectory calculations obtained by this method are compared with the Born–Oppenheimer approach (BO), in which the density is converged at each step rather than propagated. For NaCl, the vibrational frequency with ADMP is found to be independent of the fictitious electronic mass and to be equal to the BO trajectory result. For the photodissociation of formaldehyde, H2CO→H2+CO, and the three body dissociation of glyoxal, C2H2O2→H2+2CO, very good agreement is found between the Born–Oppenheimer trajectories and the extended Lagrangian approach in terms of the rotational and vibrational energy distributions of the products. A 1.2 ps simulation of the dynamics of chloride ion in a cluster of 25 water molecules was used as a third test case. The Fourier transform of the velocity–velocity autocorrelation function showed ...
TL;DR: In this article, an implementation of transition moments and excited-state first-order properties for the approximate coupled-cluster singles-and-doubles model (CC2) using the resolution of the identity (RI) approximation is reported.
Abstract: An implementation of transition moments and excited-state first-order properties is reported for the approximate coupled-cluster singles-and-doubles model (CC2) using the resolution of the identity (RI) approximation. In parallel to the previously reported code for the ground- and excited-state amplitude equations, we utilize a partitioned form of the CC2 equations and thus eliminate the need to store any N 4 intermediates. This opens the perspective for applications on molecules with 30 and more atoms. The accuracy of the RI approximation is tested for a set of 29 molecules for the aug-cc -p V X Z (X=D,T,Q) basis sets in connection with the recently optimized auxiliary basis sets. These auxiliary basis sets are found to be sufficient even for the description of diffuse states. The RI error is compared to the usual basis set error and is demonstrated to be insignificant.
TL;DR: In this paper, the performance of the previously proposed polarization consistent basis sets is analyzed at the Hartree-Fock and density functional levels of theory, and it is shown that each step up in basis set quality decreases the error relative to the infinite basis set limit by approximately an order of magnitude.
Abstract: The performance of the previously proposed polarization consistent basis sets is analyzed at the Hartree–Fock and density functional levels of theory, and it is shown that each step up in basis set quality decreases the error relative to the infinite basis set limit by approximately an order of magnitude. For the largest pc-4 basis set the relative energy error is approximately 10−7, and extrapolation further improves the results by approximately a factor of 2. This provides total atomization energies for molecules with an accuracy of better than 0.01 kJ/mol per atom. The performance of many popular basis sets is evaluated based on 95 atomization energies, 42 ionization potentials and 10 molecular relative energies, and it is shown that the pc-n basis sets in all cases provides better accuracy for a similar or a smaller number of basis functions.
TL;DR: In this paper, the authors reported accurate energy estimates for the water trimer through pentamer global ring minima and four low-lying hexamer isomers (cage, prism, book, cyclic S6) from first principles electronic structure calculations.
Abstract: We report accurate energetics for the water trimer through pentamer global ring minima and four low-lying hexamer isomers (cage, prism, book, cyclic S6) from first principles electronic structure calculations. The family of augmented correlation-consistent orbital basis sets of double through quintuple zeta quality was used in order to estimate complete basis set (CBS) limits for the cluster total association energies at the second order perturbation (MP2) level of theory. These are −15.8 kcal/mol (trimer), −27.6 kcal/mol (tetramer), −36.3 kcal/mol (pentamer), −45.9 kcal/mol (prism hexamer), −45.8 kcal/mol (cage hexamer), −45.6 kcal/mol (book hexamer), and −44.8 kcal/mol (ring S6 hexamer). Effects of higher correlation, estimated at the coupled cluster plus single and double with a perturbative estimate of the triple excitations [CCSD(T)] level of theory, as well as inclusion of estimates for core–valence correlation suggest that these estimates are accurate to within 0.2 kcal/mol.
TL;DR: In this article, the authors report the implementation of the rotatory strengths, based on time-dependent density functional theory, within the Amsterdam Density Functional program for the simulation of circular dichroism spectra of small and moderately sized organic molecules.
Abstract: We report the implementation of the computation of rotatory strengths, based on time-dependent density functional theory, within the Amsterdam Density Functional program. The code is applied to the simulation of circular dichroism spectra of small and moderately sized organic molecules, such as oxiranes, aziridines, cyclohexanone derivatives, and helicenes. Results agree favorably with experimental data, and with theoretical results for molecules that have been previously investigated by other authors. The efficient algorithms allow for the simulation of CD spectra of rather large molecules at a reasonable accuracy based on first-principles theory. The choice of the Kohn–Sham potential is a critical issue. It is found that standard gradient corrected functionals often yield the correct shape of the spectrum, but the computed excitation energies are systematically underestimated for the samples being studied. The recently developed exchange-correlation potentials “GRAC” and “SAOP” often yield much better a...
TL;DR: In this paper, the electronic structure and bonding in metal meso-tetraphenyl porphines MTPP, M=Fe, Co, Ni, Cu, Zn has been carried out using a density functional theory method.
Abstract: A systematic theoretical study of the electronic structure and bonding in metal meso-tetraphenyl porphines MTPP, M=Fe, Co, Ni, Cu, Zn has been carried out using a density functional theory method. The calculations provide a clear elucidation of the ground states for the MTPPs and for a series of [MTPP]x ions (x=2+, 1+, 1−, 2−, 3−, 4−), which aids in understanding a number of observed electronic properties. The calculation supports the experimental assignment of unligated FeTPP as 3A2g, which arises from the configuration (dxy)2(dz2)2(dxz)1(dyz)1. The calculated M–TPP binding energies, ionization potentials, and electron affinities are in good agreement with available experimental data. The influence of axial ligands and peripheral substitution by fluorine are in accord with the experimental observation that not only half-wave potentials (E1/2) of electrode reactions, but also the site of oxidation/reduction, may be dependent on the porphyrin basicity and the type of axial ligand coordination.