Showing papers on "Ab initio quantum chemistry methods published in 2009"
TL;DR: A novel coumarin-based fluorogenic probe bearing the 2-picolyl unit was developed as a fluorescent chemosensor with high selectivity and suitable affinity in biological systems toward Cu(2+) over other cations tested, and results indicate that 1 should be useful for the fluorescence microscopic imaging and the study on the biological functions of Cu( 2+.
Abstract: A novel coumarin-based fluorogenic probe bearing the 2-picolyl unit (1) was developed as a fluorescent chemosensor with high selectivity and suitable affinity in biological systems toward Cu2+ over other cations tested. The fluorescence on−off mechanism was studied by femtosecond time-resolved fluorescence (TRF) upconversion technique and ab initio calculations. The receptor can be applied to the monitoring of Cu2+ ion in aqueous solution with a pH span 4−10. To confirm the suitability of 1 for biological applications, we also employed it for the fluorescence detection of the changes of intracellular Cu2+ in cultured cells. The results indicate that 1 should be useful for the fluorescence microscopic imaging and the study on the biological functions of Cu2+.
976 citations
TL;DR: In this paper, the authors reported ab initio calculations of the two-dimensional systems (MoS and NbSe) and compared them with the electronic structure of the three-dimensional analogue of graphene.
Abstract: We report on ab initio calculations of the two-dimensional systems ${\text{MoS}}_{2}$ and ${\text{NbSe}}_{2}$, which recently were synthesized. We find that two-dimensional ${\text{MoS}}_{2}$ is a semiconductor with a gap which is rather close to that of the three-dimensional analog, and that ${\text{NbSe}}_{2}$ is a metal, which is similar to the three-dimensional analog of this compound. We further computed the electronic structure of the two-dimensional hexagonal (graphene-like) lattices of Si and Ge and compared them with the electronic structure of graphene. It is found that the properties related to the Dirac cone do not appear in the case of two-dimensional hexagonal germanium, which is metallic, contrary to two-dimensional hexagonal silicon, also known as silicene, which has an electronic structure very similar to the one of graphene, making them possibly equivalent.
924 citations
TL;DR: Nishio et al. as discussed by the authors survey recent results relevant to the CH/π hydrogen bond: crystal conformation, packing and host/guest chemistry, and summarize the results obtained by crystallographic database (CSD and PDB) analyses.
Abstract: This treatise is an update to a preceding highlight (CH/π hydrogen bonds in crystals) published in this journal 5 years ago (M. Nishio, CrystEngComm, 2004, 6, 130–156). After the introductory part (sections 1 and 2), we survey recent results (mostly since 2004) relevant to the CH/π hydrogen bond: crystal conformation, packing and host/guest chemistry (section 3). Section 4 summarizes the results obtained by crystallographic database (CSD and PDB) analyses. In section 5, several topics in related fields (selectivity in organic reactions, surface chemistry, structural biology, drug design and high-level ab initio calculations of protein/substrate complexes and natural organic compounds) are introduced, and in the final part we comment on the prospects of this emerging field of chemistry.
489 citations
TL;DR: Rehr et al. as discussed by the authors proposed ab initio calculations of the dielectric function over a broad spectrum yield system dependent self-energies and mean-free paths, as well as intrinsic losses due to multi-electron excitations.
436 citations
TL;DR: In this article, a thermodynamically rigorous continuum description of the elastic response is formulated by expanding the elastic strain energy density in a Taylor series in strain truncated after the fifth-order term.
Abstract: The nonlinear in-plane elastic properties of graphene are calculated using density-functional theory. A thermodynamically rigorous continuum description of the elastic response is formulated by expanding the elastic strain energy density in a Taylor series in strain truncated after the fifth-order term. Upon accounting for the symmetries of graphene, a total of fourteen nonzero independent elastic constants are determined by least-squares fit to the ab initio calculations. The nonlinear continuum description is valid for infinitesimal and finite strains under arbitrary in-plane tensile loading in circumstance for which the bending stiffness can be neglected. The continuum formulation is suitable for incorporation into the finite element method.
392 citations
TL;DR: In this paper, the authors constructed an interatomic potential for the Ni-Al system within the embedded-atom method formalism, based on previously developed accurate potentials for pure Ni and Al.
Abstract: We construct an interatomic potential for the Ni-Al system within the embedded-atom method formalism. The potential is based on previously developed accurate potentials for pure Ni and Al. The cross-interactions are fitted to experimental cohesive energy, lattice parameter and elastic constants of B2-NiAl, as well as to ab initio formation energies of several real or imaginary intermetallic compounds with different crystal structures and chemical compositions. The potential accurately reproduces a variety of physical properties of the NiAl and Ni3Al phases, and shows reasonable agreement with experimental and ab initio data for phase stability across the Ni-Al phase diagram. Most of the properties reproduced by the new potential were not involved in the fitting process, which demonstrates its excellent transferability. Advantages and certain weaknesses of the new potential in comparison with other existing potentials are discussed in detail. The potential is expected to be especially suitable for simulati...
317 citations
TL;DR: Results are in agreement with ab initio calculations performed using the complete active space self-consistent field (CASSCF) method, validating the predictive power of this theoretical approach for complex systems containing rare-earth ions, even in low-symmetry environments.
Abstract: A mixed theoretical and experimental approach was used to determine the local magnetic anisotropy of the dysprosium(III) ion in a low-symmetry environment. The susceptibility tensor of the monomeric species having the formula [Dy(hfac)(3)(NIT-C(6)H(4)-OEt)(2)], which contains nitronyl nitroxide (NIT-R) radicals, was determined at various temperatures through angle-resolved magnetometry. These results are in agreement with ab initio calculations performed using the complete active space self-consistent field (CASSCF) method, validating the predictive power of this theoretical approach for complex systems containing rare-earth ions, even in low-symmetry environments. Susceptibility measurements performed with the applied field along the easy axis eventually permitted a detailed analysis of the temperature and field dependence of the magnetization, providing evidence that the Dy ion transmits an antiferromagnetic interaction between radicals but that the Dy-radical interaction is ferromagnetic.
236 citations
TL;DR: The authors have found that a large number of renormalized basis states are required to represent high entanglement of the electron correlation for metal compound applications, and it is crucial to adopt auxiliary perturbative correction to the projected density matrix during the DMRG sweep optimization in order to attain proper convergence to the solution.
Abstract: This article presents an efficient and parallelized implementation of the density matrix renormalization group (DMRG) algorithm for quantum chemistry calculations. The DMRG method as a large-scale multireference electronic structure model is by nature particularly efficient for one-dimensionally correlated systems, while the present development is oriented toward applications for polynuclear transition metal compounds, in which the macroscopic one-dimensional structure of electron correlation is absent. A straightforward extension of the DMRG algorithm is proposed with further improvements and aggressive optimizations to allow its application with large multireference active space, which is often demanded for metal compound calculations. Special efficiency is achieved by making better use of sparsity and symmetry in the operator and wave function representations. By accomplishing computationally intensive DMRG calculations, the authors have found that a large number of renormalized basis states are requir...
213 citations
TL;DR: A methodology based on the Baer-Neuhauser-Livshits range-separated hybrid DFs for which Koopmans' approach "springs to life" is discussed, and a theory for the curvature of the energy as a function of fractional occupation numbers is developed.
Abstract: The meaning of orbital energies (OOEs) in Kohn-Sham (KS) density functional theory (DFT) is subject to a longstanding controversy. In local, semilocal, and hybrid density functionals (DFs) a Koopmans' approach, where OOEs approximate negative ionization potentials (IPs), is unreliable. We discuss a methodology based on the Baer-Neuhauser-Livshits range-separated hybrid DFs for which Koopmans' approach "springs to life." The OOEs are remarkably close to the negative IPs with typical deviances of +/-0.3 eV down to IPs of 30 eV, as demonstrated on several molecules. An essential component is the ab initio motivated range-parameter tuning procedure, forcing the highest OOE to be exactly equal to the negative first IP. We develop a theory for the curvature of the energy as a function of fractional occupation numbers to explain some of the results.
193 citations
TL;DR: In the garden of dispersion: high-accuracy ab initio calculations are performed to determine the nature of the interactions and the most favorable geometries between CO(2) and heteroaromatic molecules containing nitrogen.
Abstract: In the garden of dispersion: High-accuracy ab initio calculations are performed to determine the nature of the interactions and the most favorable geometries between CO(2) and heteroaromatic molecules containing nitrogen (see figure). Dispersion forces play a key role in the stabilization of the dimer, because correlation effects represent about 50 % of the total interaction energy. The interactions between carbon dioxide and organic heterocyclic molecules containing nitrogen are studied by using high-accuracy ab initio methods. Various adsorption positions are examined for pyridine. The preferred configuration is an in-plane configuration. An electron donor-electron acceptor (EDA) mechanism between the carbon of CO(2) and the nitrogen of the heterocycle and weak hydrogen bonds stabilize the complex, with important contributions from dispersion and induction forces. Quantitative results of the binding energy of CO(2) to pyridine (C(5)H(5)N), pyrimidine, pyridazine, and pyrazine (C(4)H(4)N(2)), triazine (C(3)H(3)N(3)), imidazole (C(3)H(4)N(2)), tetrazole (CH(2)N(4)), purine (C(5)H(4)N(4)), imidazopyridine (C(6)H(5)N(3)), adenine (C(5)H(5)N(5)), and imidazopyridamine (C(6)H(6)N(4)) for the in-plane configuration are presented. For purine, three different binding sites are examined. An approximate coupled-cluster model including single and double excitations with a perturbative estimation of triple excitations (CCSD(T)) is used for benchmark calculations. The CCSD(T) basis-set limit is approximated from explicitly correlated second-order Moller-Plesset (MP2-F12) calculations in the aug-cc-pVTZ basis in conjunction with contributions from single, double, and triple excitations calculated at the CCSD(T)/6-311++G** level of theory. Extrapolations to the MP2 basis-set limit coincide with the MP2-F12 calculations. The results are interpreted in terms of electrostatic potential maps and electron density redistribution plots. The effectiveness of density functional theory with the empirical dispersion correction of Grimme (DFT-D) is also examined.
178 citations
TL;DR: The composition of β″ precipitates in an Al-Mg-Si alloy has been investigated by atom probe tomography, ab initio density functional calculations, and quantitative electron diffraction.
Abstract: The composition of β″ precipitates in an Al–Mg–Si alloy has been investigated by atom probe tomography, ab initio density functional calculations, and quantitative electron diffraction. Atom probe analysis of an Al-0.72% Si-0.58% Mg (at. %) alloy heat treated at 175 °C for 36 h shows that the β″ phase contains ∼20 at. % Al and has a Mg/Si-ratio of 1.1, after correcting for a local magnification effect and for the influence of uneven evaporation rates. The composition difference is explained by an exchange of some Si with Al relative to the published β″-Mg5Si6 structure. Ab initio calculations show that replacing the Si3-site by aluminum leads to energetically favorable compositions consistent with the other phases in the precipitation sequence. Quantitative electron nanodiffraction is relatively insensitive to this substitution of Al by Si in the β″-phase.
TL;DR: Three modifications to recent ab initio, full-dimensional potential energy surfaces (PESs) for the water dimer are reported, which produce a hybrid potential that goes smoothly in the asymptotic region to the flexible, Thole-type model potential, version 3 dimer potential (denoted TTM3-F).
Abstract: We report three modifications to recent ab initio, full-dimensional potential energy surfaces (PESs) for the water dimer [X. Huang et al., J. Chem. Phys. 128, 034312 (2008)]. The first modification is a refit of ab initio electronic energies to produce an accurate dissociation energy De. The second modification adds replacing the water monomer component of the PES with a spectroscopically accurate one and the third modification produces a hybrid potential that goes smoothly in the asymptotic region to the flexible, Thole-type model potential, version 3 dimer potential (denoted TTM3-F) [G. S. Fanourgakis and S. S. Xantheas, J. Chem. Phys. 128, 074506 (2008)]. The rigorous D0 for these PESs, obtained using diffusion Monte Carlo calculations of the dimer zero-point energy, and an accurate zero-point energy of the monomer, range from 12.5 to 13.2 kJ/mol (2.99–3.15 kcal/mol), with the latter being the suggested benchmark value. For TTM3-F D0 equals 16.1 kJ/mol. Vibrational calculations of monomer fundamental e...
TL;DR: Ab initio calculations in bcc iron show that a 111 screw dislocation induces a short-range dilatation field in addition to the Volterra elastic field, which allows deriving a core energy which converges faster with the cell size, thus leading to a result which does not depend on the geometry of the dislocation array used for the simulation.
Abstract: Ab initio calculations in bcc iron show that a $⟨111⟩$ screw dislocation induces a short-range dilatation field in addition to the Volterra elastic field. This core field is modeled in anisotropic elastic theory using force dipoles. The elastic modeling thus better reproduces the atom displacements observed in ab initio calculations. Including this core field in the computation of the elastic energy allows deriving a core energy which converges faster with the cell size, thus leading to a result which does not depend on the geometry of the dislocation array used for the simulation.
TL;DR: In this paper, the authors derived effective Hubbard-type Hamiltonians of κ-(BEDT-TTF) 2 X, using an ab initio downfolding technique, for the first time for organic conductors.
Abstract: We derive effective Hubbard-type Hamiltonians of κ-(BEDT-TTF) 2 X , using an ab initio downfolding technique, for the first time for organic conductors. They contain dispersions of the highest occupied Wannier-type molecular orbitals with the nearest neighbor transfer t ∼0.067 eV for a metal X =Cu(NCS) 2 and 0.055 eV for a Mott insulator X =Cu 2 (CN) 3 , as well as screened Coulomb interactions. It shows unexpected differences from the conventional extended Huckel results, especially much stronger onsite interaction U ∼0.8 eV ( U / t ∼12–15) than the Huckel estimates ( U / t ∼7–8) as well as an appreciable longer-ranged interaction. Reexamination on physics of this family of materials is required from this realistic basis.
TL;DR: In this article, the authors used density functional theory based ab initio calculations to investigate the tendency of He and H to form clusters and found that He atoms always bond more strongly to HexHy complexes in a vacancy than H atoms.
TL;DR: The full-dimensional, ab initio potential energy (PES) and dipole moment surfaces (DMS) for water are reported and the predictive accuracy of the PES is demonstrated for the water trimer, tetramer, and hexamer by comparing the energies and harmonic frequencies obtained from the PECs and new high level abinitio calculations at the respective global minima.
Abstract: We report full-dimensional, ab initio potential energy (PES) and dipole moment surfaces (DMS) for water. The PES is a sum of one-, two- and three-body terms. The three-body potential is a fit, reported here, to roughly 30,000 intrinsic three-body energies obtained with second-order Moller–Plesset perturbation theory (MP2) and using the aug-cc-pVTZ basis set (avtz). The one- and two-body potentials are from an ab initio water dimer potential [Shank et al., J. Chem. Phys. 130, 144314 (2009)]. The predictive accuracy of the PES is demonstrated for the water trimer, tetramer, and hexamer by comparing the energies and harmonic frequencies obtained from the PES and new high level ab initio calculations at the respective global minima. The DMS is constructed from one- and two-body dipole moments, based on fits to MP2/avtz dipole moments. It is shown to be very accurate for the hexamer by comparison with direct calculations of the hexamer dipole. To illustrate the anharmonic character of the PES one-mode calculat...
TL;DR: In this article, the authors investigated the effects of hydrogen passivation of edges of armchair graphene nanoribbons (AGNRs) on their electronic properties using first-principles method and calculated band gaps of the AGNRs vary continually over a range of 1.6 eV as a function of a percentage of sp3-like bonds at the edges.
Abstract: We investigated effects of hydrogen passivation of edges of armchair graphene nanoribbons (AGNRs) on their electronic properties using first-principles method. The calculated band gaps of the AGNRs vary continually over a range of 1.6 eV as a function of a percentage of sp3-like bonds at the edges. This provides a simple way for band gap engineering of graphene as the relative stability of sp2 and sp3-like bonds at the edges of the AGNRs depends on the chemical potential of hydrogen gas, and the composition of the sp2 and sp3-like bonds at the edges of the AGNRs can be easily controlled experimentally via temperature and pressure of H2 gas.
TL;DR: Accurate aqueous-phase vertical ionization potentials provide a significant improvement to the corrected gas-phase values used in the literature and represent important information in assessing the threshold energies for photooxidation and oxidation free energies of solvent-exposed DNA components.
Abstract: Vertical ionization energies of the nucleosides cytidine and deoxythymidine in water, the lowest ones amounting in both cases to 8.3 eV, are obtained from photoelectron spectroscopy measurements in aqueous microjets. Ab initio calculations employing a nonequilibrium polarizable continuum model quantitatively reproduce the experimental spectra and provide molecular interpretation of the individual peaks of the photoelectron spectrum, showing also that lowest ionization originates from the base. Comparison of calculated vertical ionization potentials of pyrimidine bases, nucleosides, and nucleotides in water and in the gas phase underlines the dramatic effect of bulk hydration on the electronic structure. In the gas phase, the presence of sugar and, in particular, of phosphate has a strong effect on the energetics of ionization of the base. Upon bulk hydration, the ionization potential of the base in contrast becomes rather insensitive to the presence of the sugar and phosphate, which indicates a remarkable screening ability of the aqueous solvent. Accurate aqueous-phase vertical ionization potentials provide a significant improvement to the corrected gas-phase values used in the literature and represent important information in assessing the threshold energies for photooxidation and oxidation free energies of solvent-exposed DNA components. Likewise, such energetic data should allow improved assessment of delocalization and charge-hopping mechanisms in DNA ionized by radiation.
TL;DR: Molecular switches: Highly efficient acido- and photoswitchable frequency doublers (see scheme) based on the indolinooxazolidine core are studied by means of hyper-Rayleigh experiments and quantum-chemical calculations.
Abstract: Molecular switches: Highly efficient acido- and photoswitchable frequency doublers (see scheme) based on the indolinooxazolidine core are studied by means of hyper-Rayleigh experiments and quantum-chemical calculations.
To optimize the nonlinear optical (NLO) contrast, a series of indolinooxazolidine derivatives with electron-withdrawing substituents in the para position on the indolinic residue have been synthesized. Their linear and nonlinear optical properties have been characterized by UV-visible absorption and hyper-Rayleigh scattering measurements, as well as by ab initio calculations. The two-way photo- or pH-triggered switching mechanism has been demonstrated by comparing the absorption spectra of the zwitterionic and protonated open forms (POF). Hyper-Rayleigh measurements have revealed that the second-order NLO contrast between the closed indolinooxazolidine and the open π-conjugated colored forms remain very large upon substitution. Theory and measurements show that for the POFs the amplitude of the first hyperpolarizability follows the Hammett parameters of the withdrawing groups. However, because the measurements are performed in resonance, to recover this behavior, elaborate procedures including homogeneous and inhomogeneous broadenings, as well as single-mode vibronic structures are necessary to extrapolate to the static limit.
TL;DR: Unfortunately, PM2 method could not predict vibrational frequencies and visible spectra of the azo dyes under conditions of this investigation.
TL;DR: It turned out Ge/Sb deficiencies (excess) in the cubic phase induce a shift of the Fermi level inside the valence (conduction) bands outside the bandgap, while the amorphous network is flexible enough to accommodate defects in stoichiometry.
Abstract: Based on ab initio molecular dynamics simulations, we investigated the structural, electronic and vibrational properties of cubic and amorphous Ge2Sb2Te5 (GST) phase change material, focusing in particular on the effects of defects in stoichiometry on the electronic properties. It turned out Ge/Sb deficiencies (excess) in the cubic phase induce a shift of the Fermi level inside the valence (conduction) bands. In contrast, the amorphous network is flexible enough to accommodate defects in stoichiometry, keeping the Fermi level pinned at the center of the bandgap (at zero temperature). Changes in the structural and electronic properties induced by the use of hybrid functionals (HSE03, PBE0) instead of gradient corrected functionals (PBE) are addressed as well. Analysis of vibrational spectra and Debye–Waller factors of cubic and amorphous GST is also presented.
TL;DR: A theoretical investigation of electronic and optical properties of free-base porphyrins based on density functional theory and many-body perturbation theory is presented and results that compare favorably with the available photoemission spectra are found.
Abstract: We present a theoretical investigation of electronic and optical properties of free-base porphyrins based on density functional theory and many-body perturbation theory. The electronic levels of free-base porphine H2P and its phenyl derivative, free-base tetraphenylporphyrin H2TPP are calculated using the ab initio GW approximation for the self-energy. The approach is found to yield results that compare favorably with the available photoemission spectra. The excitonic nature of the optical peaks is revealed by solving the Bethe–Salpeter equation, which provides an accurate description of the experimental absorption spectra. The lowest triplet transition energies are in good agreement with the measured values. © 2009 American Institute of Physics. DOI: 10.1063/1.3204938
TL;DR: An accurate full-dimensional global potential energy surface (PES) for the F+CH(4)-->HF+CH (3) reaction has been developed based on 19 384 UCCSD(T)/aug-cc-pVTZ quality ab initio energy points obtained by an efficient composite method employing explicit UCC SDZ and UMP2/aug-CC-pVXZ [X=D,T] computations.
Abstract: An accurate full-dimensional global potential energy surface (PES) for the F+CH4→HF+CH3 reaction has been developed based on 19 384 UCCSD(T)/aug-cc-pVTZ quality ab initio energy points obtained by an efficient composite method employing explicit UCCSD(T)/aug-cc-pVDZ and UMP2/aug-cc-pVXZ [X=D,T] computations. The PES contains a first-order saddle point, (CH4- -F)SP, separating reactants from products, and also minima describing the van der Waals complexes, (CH4- - -F)vdW and (CH3- - -HF)vdW, in the entrance and exit channels, respectively. The structures of these stationary points, as well as those of the reactants and products have been computed and the corresponding energies have been determined using basis set extrapolation techniques considering (a) electron correlation beyond the CCSD(T) level, (b) effects of the scalar relativity and the spin-orbit couplings, (c) diagonal Born–Oppenheimer corrections (DBOC), and (d) zero-point vibrational energies and thermal correction to the enthalpy at 298 K. The ...
TL;DR: In this article, a series of quartic force fields (QFFs) were computed using a procedure recently proposed for NH2− and CCH− using a single and doubles coupled-cluster method with a perturbational estimate of the effects of connected triple excitations, denoted CCSD(T), was used with TZ, QZ, and 5Z quality basis sets and was combined with extrapolation to the one-particle basis set limit, core-correlation effects, scalar relativistic effects, and higher-order correlation effects to
Abstract: A series of high-quality, purely ab initio, quartic force fields (QFFs), computed using a procedure we recently proposed, is reported for NH2− and CCH−. The singles and doubles coupled-cluster method with a perturbational estimate of the effects of connected triple excitations, denoted CCSD(T), was used with TZ, QZ, and 5Z quality basis sets and was combined with extrapolation to the one-particle basis-set limit, core-correlation effects, scalar relativistic effects, and higher-order correlation effects to yield accurate QFFs. A “best-guess” reference geometry was determined at the CCSD(T)/5Z level of theory. Analytical transformation removes nonzero gradients to facilitate a second-order perturbation theory spectroscopic analysis. The QFF is transformed into Morse/cosine coordinates in order to perform exact vibrational configuration interaction computations. Equilibrium structures, vibrational frequencies, rotational constants, and selected spectroscopic constants are reported in comparison with experim...
TL;DR: The purpose of this work is to compare the two different procedures to calculate the L(2,3) x-ray absorption spectra of transition-metal compounds: (1) the semi-empirical charge transfer multiplet (CTM) approach and (2) the ab initio configuration-interaction (CI) method based on molecular orbitals.
Abstract: The purpose of this work is to compare the two different procedures to calculate the L2,3 x-ray absorption spectra of transition-metal compounds: (1) the semi-empirical charge transfer multiplet (CTM) approach and (2) the ab initio configuration-interaction (CI) method based on molecular orbitals. We mainly focused on the difference in the treatment of ligand field effects and the charge transfer effects in the two methods. The reduction of multiplet interactions due to the solid state effects has been found by the ab initio CI approach. We have also found that the mixing between the original and the charge transferred configurations obtained by the ab initio CI approach is smaller than that obtained by the CTM approach, since charge transfer through the covalent bonding between metal and ligand atoms has been included by taking the molecular orbitals as the basis functions. (Some figures in this article are in colour only in the electronic version)
TL;DR: In this paper, the second-, third-, and fourth-order elastic constants of single crystals with arbitrary symmetry were calculated by employing ab initio density-functional theory, which utilizes a series of homogeneous deformation strains applied to a crystalline system to obtain the internal energy-strain relations.
Abstract: We present a general scheme to calculate the second-, third-, and fourth-order elastic constants of single crystals with arbitrary symmetry by employing ab initio density-functional theory. The method utilizes a series of homogeneous deformation strains applied to a crystalline system to obtain the internal energy-strain relations. From the nonlinear least-squares fitting, we obtain the elastic constants from the coefficients of the fitted polynomials of the internal energy functions. We applied this method first to four fcc metal crystals, Cu, Al, Au, and Ag. The calculated second-, third-, and fourth-order elastic constants are compared with the available experimental data and other theoretical calculations and found very good agreement. Since accurate determination of higher-order elastic constants, in particular, the fourth-order elastic constants from experiment, is still a challenge, the theoretical approach presented here is certainly of a great help to fill the gap.
TL;DR: In this paper, the authors apply ab initio molecular dynamics (AIMD) methods in conjunction with the thermodynamic integration or "lambda-path" technique to compute the intrinsic hydration free energies of Li(+), Cl(-), and Ag(+) ions.
Abstract: We apply ab initio molecular dynamics (AIMD) methods in conjunction with the thermodynamic integration or "lambda-path" technique to compute the intrinsic hydration free energies of Li(+), Cl(-), and Ag(+) ions. Using the Perdew-Burke-Ernzerhof functional, adapting methods developed for classical force field applications, and with consistent assumptions about surface potential (phi) contributions, we obtain absolute AIMD hydration free energies (DeltaG(hyd)) within a few kcal/mol, or better than 4%, of Tissandier et al.'s [J. Phys. Chem. A 102, 7787 (1998)] experimental values augmented with the SPC/E water model phi predictions. The sums of Li(+)/Cl(-) and Ag(+)/Cl(-) AIMD DeltaG(hyd), which are not affected by surface potentials, are within 2.6% and 1.2 % of experimental values, respectively. We also report the free energy changes associated with the transition metal ion redox reaction Ag(+)+Ni(+)-->Ag+Ni(2+) in water. The predictions for this reaction suggest that existing estimates of DeltaG(hyd) for unstable radiolysis intermediates such as Ni(+) may need to be extensively revised.
TL;DR: In this paper, the authors obtained new thermochemical data for 5-hydroxymethylfurfural (HMF) and parent compounds and verified the experimental data using ab initio calculations of all compounds.
Abstract: This work was undertaken to obtain new thermochemical data for 5-hydroxymethylfurfural (HMF) and parent compounds The standard molar enthalpy of formation in the gaseous state of HMF was obtained from combustion calorimetry, differential scanning calorimetry (DSC), and measurements of the temperature dependence of the vapor pressure by the transpiration method To verify the experimental data, ab initio calculations of all compounds were performed Enthalpies of formation derived from the G3MP2 method are in an excellent agreement with the experimental results A weak hydrogen bond in HMF was revealed using ab initio methods Thermodynamic analysis of the transformation of HMF to the bulk intermediates according to hydrogenation and oxidation pathways has revealed a very high feasibility of these reactions, with equilibrium constants that are completely shifted to the desired reaction products even at 298 K
TL;DR: In this article, first-principles calculations for clean and In-rich GaN(1122) surfaces indicate that indium will, for the same indium chemical potential, incorporate in higher concentrations on the 1122 surface than on the (1010) surface.
Abstract: First-principles calculations for clean and In-rich GaN(1122) surfaces indicate that indium will, for the same indium chemical potential, incorporate in higher concentrations on the (1122) surface than on the (1010) surface. Because In atoms are larger than Ga atoms, there is a strain-induced repulsive interaction between incorporated In atoms on the surface. This interaction is weaker on the (1122) surface in comparison to the (1010) surface.
TL;DR: In this article, the authors describe a method for calculating temperature dependent phonon spectra self consistently from first principles, combining concepts from Born's self-consistent phonon approach with ab initio calculations of accurate interatomic forces in a supercell.