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Showing papers in "International Journal of Quantum Chemistry in 1998"


Journal ArticleDOI
TL;DR: In this article, a clutch of '-isms' characterises the approach to consciousness which David Chalmers defends: dualism, epiphenomenalism, functionalism, anti-reductionism, and -probably -panpsychism.
Abstract: A clutch of '-isms' characterises the approach to consciousness which David Chalmers defends: dualism, epiphenomenalism, functionalism, anti-reductionism, and -probably -panpsychism. (The author would no doubt want 'naturalism' included in the list as well, but as we shall see, Chalmers' predilection to describe his theory as 'scientific' stretches credibility.) While the book does not, as far as I can see, move consciousness research significantly forward, Chalmers succeeds admirably in clarifying the philosophical terrain around and within each of these '-isms' and in questioning the usual assumptions which suggest some of them are mutually exclusive. Because nearly all of what follows is highly critical, I want to be explicit about one thing: I do not think this is a bad book. Throughout, most discussions keep to a very high standard; it's just that they include fatal flaws.

911 citations


Journal ArticleDOI
TL;DR: In this article, it is demonstrated that frequency-dependent response functions can be derived from the time-averaged quasienergy, which plays the same role as the usual energy in time-independent theory, and the same techniques can be used to obtain computationally tractable expressions for response properties, as for energy derivatives in timeindependent theory.
Abstract: It is demonstrated that frequency-dependent response functions can conveniently be derived from the time-averaged quasienergy The variational criteria for the quasienergy determines the time-evolution of the wave-function parameters and the time-averaged time-dependent Hellmann)Feynman theorem allows an identification of response functions as derivatives of the quasienergy The quasienergy therefore plays the same role as the usual energy in time-independent theory, and the same techniques can be used to obtain computationally tractable expressions for response properties, as for energy derivatives in time-independent theory This includes the use of the variational Lagrangian technique for obtaining expressions for molecular properties in accord with the 2 n q 1 and 2 n q 2 rules The derivation of frequency-dependent response properties becomes a simple extension of variational perturbation theory to a Fourier component variational perturbation theory The generality and simplicity of this approach are illustrated by derivation of linear and higher-order response functions for both exact and approximate wave functions and for both variational and nonvariational wave functions Examples of approximate models discussed in this article are coupled-cluster, self- consistent field, and second-order Moller)Plesset perturbation theory A discussion of symmetry properties of the response functions and their relation to molecular properties is also given, with special attention to the calculation of transition- and excited-state

509 citations


Journal ArticleDOI
TL;DR: In this paper, the atomic characteristics which govern changes in bonding properties due to relativistic effects in heavy atoms are identified from a scattering theoretic standpoint, and it is shown that within an all-electron calculation scalar relatival corrections to valence orbitals relevant to atomic bonding properties can be made via a local pseudopotential for all elements.
Abstract: The atomic characteristics, which govern changes in bonding properties due to relativistic effects in heavy atoms, are identified from a scattering theoretic standpoint. It is shown that within an all-electron calculation scalar relativistic corrections to valence orbitals relevant to atomic bonding properties can be made via a local pseudopotential for all elements. The present approach reproduces molecular geometries and vibrational frequencies excellently for a test set of relatively simple molecules, where good experimental data are available. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 69: 423–433, 1998

249 citations


Journal ArticleDOI
TL;DR: In this article, the first density-functional theory (DFT) treatment of excited-state potential energy surfaces exhibiting avoided crossings was reported, and the results were compared with multireference doubles configuration interaction (MRD-CI) results for the 1A1 manifold of the CO stretching curves of planar formaldehyde.
Abstract: This work reports the first density-functional theory (DFT) treatment of excited-state potential energy surfaces exhibiting avoided crossings. Time-dependent DFT (TD-DFT) results, using a recently proposed asymptotically corrected local density approximation functional, are compared with multireference doubles configuration interaction (MRD-CI) results for the 1A1 manifold of the CO stretching curves of planar formaldehyde. TD-DFT is found to reproduce the qualitative features essential for understanding the spectroscopy of this manifold, specifically the strong mixing of the 1(π, π*) with Rydberg transitions and the resultant avoided crossings. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 933–941, 1998

202 citations


Journal ArticleDOI
TL;DR: In this paper, a new way of analyzing measured or calculated vibrational spectra in terms of internal vibrational modes associated with the internal parameters used to describe geometry and conformation of a molecule is described.
Abstract: A new way of analyzing measured or calculated vibrational spectra in terms of internal vibrational modes associated with the internal parameters used to describe geometry and conformation of a molecule is described. The internal modes are determined by solving the Euler–Lagrange equations for molecular fragments ϕn described by internal parameters ζn. An internal mode is localized in a molecular fragment by describing the rest of the molecule as a collection of massless points that just define molecular geometry. Alternatively, one can consider the new fragment motions as motions that are obtained after relaxing all parts of the vibrating molecule but the fragment under consideration. Because of this property, the internal modes are called adiabatic internal modes, and the associated force constants ka, adiabatic force constants. Minimization of the kinetic energy of the vibrating fragment ϕn yields the adiabatic mass ma (corresponding to 1/Gnn of Wilson's G matrix) and, by this, adiabatic frequencies ωa. Adiabatic modes are perfectly suited to analyze and understand the vibrational spectra of a molecule in terms of internal parameter modes in the same way as one understands molecular geometry in terms of internal coordinates. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 67: 1–9, 1998

180 citations


Journal ArticleDOI
TL;DR: In this paper, the optical properties of the lead chalcogenides PbS, PbSe, and PbTe were investigated using a relativistic full-potential linear muffin-tin orbital method within the local density approximation.
Abstract: We report on ab initio calculations of the optical properties of the lead chalcogenides PbS, PbSe, and PbTe performed with a relativistic full-potential linear muffin-tin orbital method within the local density approximation. Our calculated spectra are in excellent agreement with recent ellipsometry measurements. The origin of the peaks in the spectra is discussed, as well as the effects of increasing the chalcogen atomic number. Q 1998 John Wiley & Sons, Inc. Int J Quant Chem 69: 349)358, 1998

171 citations


Journal ArticleDOI
TL;DR: In this paper, an average local ionization energy defined within the framework of Hartree-Fock theory is physically meaningful in Kohn-Sham density functional theory, in view of the uncertainty in relating the latter orbital energies to electronic ionization energies.
Abstract: We investigated whether an average local ionization energy defined within the framework of Hartree–Fock theory is physically meaningful in Kohn–Sham density functional theory, in view of the uncertainty in relating the latter orbital energies to electronic ionization energies. In a preliminary study of N2O using several different exchange/correlation functional combinations, it was found that the orbital energies in each case correlate roughly with experimental binding energies. Average local ionization energies are computed on the molecular surfaces of 11 monosubstituted benzene derivatives using both Hartree–Fock and density functional procedures. Both sets of results correctly predict the ortho/para- or meta-directing tendencies of the substituents, as well as their ring-activating or -deactivating effects. Excellent correlations were obtained with the Hammett substituent constants. This initial study suggests that Kohn–Sham average local ionization energies should be physically meaningful, on a relative basis. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 69: 607–613, 1998

154 citations


Journal ArticleDOI
TL;DR: In this article, a multireference perturbation theory with complete active space self-consistent field (CASSCF) reference functions is applied to the study of the valence ππ* excited states of 1, 3-butadiene, 1,3, 5-hexatriene, and 1, 5, 7-octatetraene.
Abstract: Multireference perturbation theory with complete active space self-consistent field (CASSCF) reference functions is applied to the study of the valence ππ* excited states of 1,3-butadiene, 1,3,5-hexatriene, 1,3,5,7-octatetraene, and 1,3,5,7,9-decapentaene. Our focus was put on determining the nature of the two lowest-lying singlet excited states, 11Bu+ and 21Ag−, and their ordering. The 11Bu+ state is a singly excited state with an ionic nature originating from the HOMOLUMO one-electron transition while the covalent 21Ag− state is the doubly excited state which comes mainly from the (HOMO)2(LUMO)2 transition. The active-space and basis-set effects are taken into account to estimate the excitation energies of larger polyenes. For butadiene, the 11Bu+ state is calculated to be slightly lower by 0.1 eV than the doubly excited 21Ag− state at the ground-state equilibrium geometry. For hexatriene, our calculations predict the two states to be virtually degenerate. Octatetraene is the first polyene for which we predict that the 21Ag− state is the lowest excited singlet state at the ground-state geometry. The present theory also indicates that the 21Ag− state lies clearly below the 11Bu+ state in decapentaene with the energy gap of 0.4 eV. The 0–0 transition and the emission energies are also calculated using the planar C2h relaxed excited-state geometries. The covalent 21Ag− state is much more sensitive to the geometry variation than is the ionic 11Bu+ state, which places the 21Ag− state significantly below the 11Bu+ state at the relaxed geometry. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 66: 157–175, 1998

149 citations



Journal ArticleDOI
TL;DR: In this paper, the authors compared solid and cluster models of zeolites, and compared the substitution Si4+Al3++H+ on the T1 site of mordenite in the dilute limit using a self-consistent, full potential, local density functional (LDF) approach.
Abstract: In order to compare solid and cluster models of zeolites, we have studied the substitution Si4+Al3++H+ on the T1 site of mordenite in the dilute limit using a self-consistent, full potential, local density functional (LDF) approach. Clusters size ranged from 9 to 105 atoms. Two crystal models with different Al concentrations were used. The first contained one substitution site per primitive cell of 72 atoms, the other one per conventional cell, containing 144 atoms. The unrelaxed substitution energies as computed with cluster and crystal models correspond well if the cluster results are extrapolated to infinite radius. Size effects are much smaller in crystal models. In addition, a structure relaxation (with fixed unit cell) was carried out for pure-silica offretite, a zeolite with 54 atoms per unit cell, and pure-silica mordenite, with 144 atoms per unit cell, starting from the low aluminum content X-ray crystallographic structure. In the offretite and mordenite optimizations full use was made of the D3h1–Pm2 and the nonsymmorphic D2h17–Cmcm space group symmetry, respectively. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 68: 135–144, 1998

126 citations


Journal ArticleDOI
TL;DR: In this article, the effect of picture change on expectation values of one-electron operators in approximate two-one-component relativistic theories was discussed, and it was concluded that accurate calculations of expectation values for operators involving high inverse powers of the electron-nucleus distance must be taken into account.
Abstract: The effect of the so-called picture change on expectation values of one-electron operators in approximate two(one)-component relativistic theories is discussed. This effect is expected to be particularly large for operators which assume large values in the vicinity of heavy nuclei. The numerical results illustrating the picture change effect on electric field gradients at nuclei have been obtained in the spin-free Pauli and Douglas–Kroll approximations. It has been found that the picture change effect lowers the electric field gradient at I in HI by about 1 a.u. Very large picture change effect (−8 a.u.) has been calculated for HAt. It is concluded that in accurate calculations of expectation values of operators involving high inverse powers of the electron–nucleus distance the picture change, which accompanies the transformation of the Dirac (Dirac–Coulomb) equation to approximate two(one)-component relativistic Hamiltonians, must be taken into account. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 68: 159–174, 1998

Journal ArticleDOI
TL;DR: In this article, the concept of characterizing normal vibrational modes l in terms of m internal vibrational mode v typical of molecular fragments or structural subunits is developed, and the amplitude A that provides the basis for a nm quantitative comparison of modes l and v and facilitates the extraction of m n chemical information out of vibrational spectra.
Abstract: The concept of characterizing normal vibrational modes l in terms of m internal vibrational modes v typical of molecular fragments or structural subunits is n developed. Essential for this concept is the amplitude A that provides the basis for a nm quantitative comparison of modes l and v and, by this, facilitates the extraction of m n chemical information out of vibrational spectra. Twelve possibilities of defining amplitude . .


Journal ArticleDOI
TL;DR: In this paper, the Hellmann-Feynman theorem is used to define an adiabatic coupling between a noninteracting reference system and the real one, and it is shown that when the operator added is shifting upward the virtual (noninteracting) levels the correlation energy is related to the number of electrons displaced into the virtual levels.
Abstract: Adding a nonlocal operator to the true Hamiltonian is used to define an adiabatic coupling between a noninteracting (e.g., Kohn–Sham) reference system and the real one. By using the Hellmann–Feynman theorem, it is shown that when the operator added is shifting upward the virtual (noninteracting) levels the correlation energy is related to the number of electrons displaced into the virtual levels. To construct approximations, calculations were performed for the uniform electron gas. The expectation that atomic systems would behave locally like a uniform electron gas with the unoccupied levels shifted up by a constant close to the atomic excitation energies is not confirmed by exploratory calculations on atoms. Some perturbation theory expressions are also given and suggest an approach to self-interaction free-correlation energy functionals. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 69: 581–590, 1998

Journal ArticleDOI
TL;DR: In this article, a generalized simulated annealing (GSA) algorithm was proposed for quantum chemistry and its utility in quantum chemistry was shown through the use of a semi-empirical quantum method.
Abstract: On statistical-mechanical grounds, a stochastic optimization technique (generalized simulated annealing) has been recently proposed which contains both classical simulated annealing (Kirkpatrick et al., 1983) and fast simulated annealing (Szu, 1986) as particular cases. This technique can be faster than both in detecting global (and also local) minima. Its utility in quantum chemistry is here illustrated, through the use of a semiempirical quantum method, on molecules of the series CH3-R (C2H6, CH3COH, CH3OH), H2X2 (H2O2, H2S2), X2Y4 (N2H4, P2H4, N2F4), for double bonds (C2H4 and CH2NH), and finally for H2O3. © 1996 John Wiley & Sons, Inc.

Journal ArticleDOI
TL;DR: Adiabatic internal frequencies are compared with c-vector frequencies and intrinsic frequencies in this paper, and it is shown that cvector modes are not suitable to characterize molecular fragments f since they are not localized in f and their definition leads to nn unreasonable frequency values.
Abstract: Adiabatic internal frequencies are compared with c-vector frequencies and intrinsic frequencies. It is shown that c-vector modes are not suitable to characterize molecular fragments f since they are not localized in f and their definition leads to nn unreasonable frequency values. Intrinsic frequencies suffer from a strong dependence on the set of internal parameters chosen to describe the geometry of the molecule. Apart from this, they represent averaged frequencies, for which mass effects and electronic effects are not properly separated. Adiabatic frequencies are based on a dynamic principle, separate properly mass effects and electronic effects and do not depend in any

Journal ArticleDOI
TL;DR: In this paper, a new TS optimization method has been proposed on a multidimensional free energy surface (FES), which utilizes force and Hessian on the FES, which can be calculated by molecular dynamics method and the free energy perturbation theory.
Abstract: To obtain a transition state (TS) in solution chemical reaction, a new TS optimization method has been proposed on a multidimensional free energy surface (FES). Analogous to the method for the Born–Oppenheimer potential energy surface using ab initio molecular orbital calculation, the present method utilizes force and Hessian on the FES, which can be calculated by molecular dynamics method and the free energy perturbation theory. Furthermore, on the basis of the method, we have proposed the definition of the intrinsic reaction coordinate (IRC) on the FES. According to not only the estimation of the computational demand but also the comparison of the numerical accuracy, we conclude that our method should be more efficient than such other methods that utilize only the free energy. Finally, it is discussed that the TS optimization and the IRC on the FES should become very important tools to develop a new research field called the solution chemical reaction ergodography. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 95–103, 1998

Journal ArticleDOI
TL;DR: In this article, the CNM characterization of normal modes method for extracting chemical information out of vibrational spectra is tested for molecules with relatively strong or relatively weak coupling between internal vibrational modes.
Abstract: The CNM characterization of normal modes method for extracting chemical information out of vibrational spectra is tested for vibrational spectra of molecules with relatively strong or relatively weak coupling between internal vibrational modes. Symmetry, parameter set stability, and frequency uncertainty tests are applied to check whether internal vibrational modes, internal mode frequencies, and amplitudes A comply with symmetry, are independent of the set of internal parameters O used to nU n describe molecular geometry or fulfill a Lorentzian correlation between amplitudes AnU and frequency differences a a â a a a . In all cases considered, amplitudes A nU n U n U based on adiabatic internal modes and mass or force constant matrices as metric O are superior to any other definition of amplitude. They represent the basic elements of the new CNM method that leads to chemically reasonable results and presents a new way of extracting chemical information out of vibrational spectra. A number of deficiencies of e. the potential energy distribution PED analysis is discussed. a 1998 John Wiley & Sons, Inc. Int J Quant Chem 67 :4 1 a55, 1998

Journal ArticleDOI
TL;DR: In this article, the optimal Gaussian-type orbital (GTO) basis sets of positron and electron in positron-molecule complexes are proposed by using the full variational treatment of molecular orbital (FVMO) method.
Abstract: Optimal Gaussian-type orbital (GTO) basis sets of positron and electron in positron-molecule complexes are proposed by using the full variational treatment of molecular orbital (FVMO) method. The analytical expression for the energy gradient with respect to parameters of positronic and electronic GTO such as the orbital exponents, the orbital centers, and the linear combination of atomic orbital (LCAO) coefficients, is derived. Wave functions obtained by the FVMO method include the effect of electronic or positronic orbital relaxation explicitly and satisfy the virial and Hellmann–Feynman theorems completely. We have demonstrated the optimization of each orbital exponent in various positron-atomic and anion systems, and estimated the positron affinity (PA) as the difference between their energies. Our PA obtained with small basis set is in good agreement with the numerical Hartree–Fock result. We have calculated the OH− and [OH−; e+] species as the positron-molecular system by the FVMO method. This result shows that the positronic basis set not only becomes more diffuse but also moves toward the oxygen atom. Moreover, we have applied this method to determine both the nuclear and electronic wave functions of LiH and LiD molecules simultaneously, and obtained the isotopic effect directly. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 491–501, 1998


Journal ArticleDOI
TL;DR: An exact expression for the exchange kernel of time-dependent density-functional theory, the frequency-dependent functional derivative of the exchange potential with respect to the density, is derived in this paper.
Abstract: An exact expression for the exchange kernel of time-dependent density-functional theory, the frequency-dependent functional derivative of the exchange potential with respect to the density, is derived. The expression is simple enough to be applied in practice. A simple and transparent derivation of the coupled Kohn–Sham equation of time-dependent density-functional theory is given. Modified coupled Kohn–Sham equations are presented that are especially well suited for an “exact-exchange” treatment of excitation energies, polarizabilities, and other linear response properties. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 69: 265–277, 1998




Journal ArticleDOI
TL;DR: In this article, the spin-orbit effects were found to significantly stabilize Rn2 and RnXe and the van der Waals C6 and C8 coefficients, which were in good agreement with both experiment and TDMP2 calculations, were obtained from calculations at large distances.
Abstract: Counterpoise-corrected supermolecular calculations on the title molecules at MP2, CCSD, and CCSD(T) levels are used to extract a van der Waals radius of 224 pm for Rn, 6 pm more than for Xe. The spin–orbit effects are found to significantly stabilize Rn2 and RnXe. Van der Waals C6 and C8 coefficients, which are in good agreement with both experiment and TDMP2 calculations, were obtained from calculations at large distances. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 66: 131–140, 1998

Journal ArticleDOI
TL;DR: In this article, the Car-Parrinello molecular dynamics was used to compute the minimum energy structures of O2, CO, and NO iron-porphyrin (FeP) complexes.
Abstract: Minimum-energy structures of O2, CO, and NO iron–porphyrin (FeP) complexes, computed with the Car–Parrinello molecular dynamics, agree well with the available experimental data for synthetic heme models. The diatomic molecule induces a 0.3–0.4 A displacement of the Fe atom out of the porphyrin nitrogen (Np) plane and a doming of the overall porphyrin ring. The energy of the iron–diatomic bond increases in the order Fe(SINGLE BOND)O2 (9 kcal/mol) < Fe(SINGLE BOND)CO (26 kcal/mol) < Fe(SINGLE BOND)NO (35 kcal/mol). The presence of an imidazole axial ligand increases the strength of the Fe(SINGLE BOND)O2 and Fe(SINGLE BOND)CO bonds (15 and 35 kcal/mol, respectively), with few structural changes with respect to the FeP(CO) and FeP(O2) complexes. In contrast, the imidazole ligand does not affect the energy of the Fe(SINGLE BOND)NO bond, but induces significant structural changes with respect to the FeP(NO) complex. Similar variations in the iron–imidazole bond with respect to the addition of CO, O2, and NO are also discussed. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 69: 31–35, 1998


Journal ArticleDOI
TL;DR: In this article, two alternative treatments of the BSSE problem of intermolecular interactions, the a posteriori counterpoise (CP) correction scheme of Boys and Bernardi (BB) and the a priori exclusion of the basic-set superposition error (BSSE) by using the "chemical Hamiltonian approach" (CHA), are discussed.
Abstract: The two alternative treatments of the BSSE problem of intermolecular interactions—the a posteriori counterpoise (CP) correction scheme of Boys and Bernardi (BB) and the a priori exclusion of the basic-set superposition error (BSSE) by using the “chemical Hamiltonian approach” (CHA)—are discussed. Alternative interpretations of the BB scheme are compared and some problems and paradoxes are described which can consistently be resolved by introducing a hierarchical scheme of N-body CP corrections. In CHA, one identifies those terms of the Hamiltonian (or Fockian) which cause the BSSE—the same terms cause the energy lowering in the “ghost orbitals” calculations; by omitting these terms from the Hamiltonian (Fockian), one can calculate BSSE-free wave functions, by use of which the BSSE-free values of the energy and of other physical quantities can be obtained in a conventional manner. CHA was successfully applied at the SCF and DFT levels of theory, including systems containing three or more interacting subsystems or even infinite periodic chains. The pivot full CI calculations performed for small model systems showed the applicability of the approach for treating electron correlation as well. Most recently, a CHA version of the MP2 theory and a second-order BSSE-free intermolecular PT have also been tested; they are also applicable for complexes of larger size. It was observed, at any level of theory, that the results given by the a posteriori BB and a priori CHA schemes converge to each other much faster than BSSE disappears from the uncorrected results. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 41–63, 1998

Journal ArticleDOI
TL;DR: In this article, the Ghosh-Berkowitz-Parr macroscopic thermodynamic description of an electronic ground state is reviewed and the information entropy defined in this theory is calculated for several atoms using Hartree-Fock and double-zeta wave functions.
Abstract: The Ghosh-Berkowitz-Parr macroscopic thermodynamic description of an electronic ground state is reviewed. The information entropy defined in this theory is calculated for several atoms using Hartree-Fock and double-zeta wave functions. It is shown that the information entropy is a measure of wave function quality provided that a particularly preferred definition of the local kinetic energy density is implied. © 1996 John Wiley & Sons, Inc.