| 1. |
- Keal, T. W., et al.
(författare)
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Choice of exchange-correlation functional for computing NMR indirect spin-spin coupling constants
- 2006
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 425:1-3, s. 163-166
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Tidskriftsartikel (refereegranskat)abstract
- The choice of exchange-correlation functional for the determination of indirect nuclear spin-spin coupling constants in density-functional theory is considered. In an assessment of one-bond (1)J(CH) couplings, the PBE functional was recently shown [S.N. Maximoff, J.E. Peralta, V. Barone, G.E. Scuseria, J. Chem. Theory Comput. 1 (2005) 541] to perform well, significantly outperforming B3LYP. For couplings involving N, 0, and F atoms in simple molecules, we demonstrate that the opposite is observed; PBE is considerably less accurate than B3LYP. By contrast, the B97-2 and B97-3 semi-empirical functionals provide good, consistent quality couplings for all these atom types in an extensive assessment.
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| 2. |
- Peach, M. J. G., et al.
(författare)
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Assessment of a Coulomb-attenuated exchange-correlation energy functional
- 2005
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 8:5
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Tidskriftsartikel (refereegranskat)abstract
- The recently proposed CAM-B3LYP exchange-correlation energy functional, based on a partitioning of the r(12)(-1) operator in the exchange interaction into long- and short-range components, is assessed for the determination of molecular thermochemistry, structures, and second order response properties. Rydberg and charge transfer excitation energies and static electronic polarisabilities are notably improved over the standard B3LYP functional; classical reaction barriers also improve. Ionisation potentials, bond lengths, NMR shielding constants and indirect spin-spin coupling constants are comparable with the two functionals. CAM-B3LYP atomisation energies and diatomic harmonic vibrational wavenumbers are less accurate than those of B3LYP. Future research directions are outlined.
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| 3. |
- Ruud, K., et al.
(författare)
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Generalized integral-screening for efficient calculations of nonlinear optical properties of large molecules
- 1998
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 108:19, s. 7973-7979
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Tidskriftsartikel (refereegranskat)abstract
- We describe the implementation of integral screening in the integral-direct SCF calculation of cubic response functions. The screening is applied to all computational steps that involve the construction of Fock matrices or one-index transformed Fock matrices. We apply this implementation to study the length dependence of the polarizability and second hyperpolarizability of diphenylpolyenes. It is demonstrated that calculations of the second hyperpolarizability of molecules containing more than 140 atoms are now accessible by ab initio methods on a time scale that makes it of interest in real applications.
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| 4. |
- Salek, Pawel, et al.
(författare)
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Linear response at the 4-component relativistic density-functional level : application to the frequency-dependent dipole polarizability of Hg, AuH and PtH2
- 2005
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Ingår i: Chemical Physics. - : Elsevier BV. - 0301-0104 .- 1873-4421. ; 311:1-2, s. 187-201
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Tidskriftsartikel (refereegranskat)abstract
- We report the implementation and application of linear response density-functional theory (DFT) based on the 4-component relativistic Dirac-Coulomb Hamiltonian. The theory is cast in the language of second quantization and is based on the quasienergy formalism (Floquet theory), replacing the initial state dependence of the Runge-Gross theorem by periodic boundary conditions. Contradictions in causality and symmetry of the time arguments are thereby avoided and the exchange-correlation potential and kernel can be expressed as functional derivatives of the quasienergy. We critically review the derivation of the quasienergy analogues of the Hohenberg-Kohn theorem and the Kohn-Sham formalism and discuss the nature of the quasienergy exchange-correlation functional. Structure is imposed on the response equations in terms of Hermiticity and time-reversal symmetry. It is observed that functionals of spin and current densities, corresponding to time-antisymmetric operators, contribute to frequency-dependent and not static electric properties. Physically, this follows from the fact that only a time-dependent electric field creates a magnetic field. It is furthermore observed that hybrid functionals enhance spin polarization since only exact exchange contributes to anti-Hermitian trial vectors. We apply 4-component relativistic linear response DFT to the calculation of the frequency-dependent polarizability of the iso-electronic series Hg, AuH and PtH2. Unlike for the molecules, the effect of electron correlation on the polarizability of the mercury atom is very large, about 25%. We observe a remarkable performance of the local-density approximation (LDA) functional in reproducing the experimental frequency-dependent polarizability of this atom, clearly superior to that of the BLYP and B3LYP functionals. This allows us to extract Cauchy moments (S(-4) = 382.82 and S(-6) = 6090.89 a.u.) that we believe are superior to experiment since we go to higher order in the Cauchy moment expansion.
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| 5. |
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| 6. |
- Christiansen, Ove, et al.
(författare)
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Vibronic transitions from coupled-cluster response theory: Theory and application to HSiF and H2O
- 2002
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Ingår i: Journal of Chemical Physics. - 0021-9606. ; 116:19, s. 8334-8342
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Tidskriftsartikel (refereegranskat)abstract
- A scheme for calculating the vibrational structure of electronic spectra using coupled-cluster response theory is proposed. To calculate the vibrational structure of electronic transitions, the optimized geometries of the two electronic states, the molecular Hessians, the dipole transition moment and (for vibrationally induced transitions) the geometrical gradient of the dipole transition moment are used in conjunction with a recently developed method for the evaluation of Franck-Condon factors of multidimensional harmonic oscillators. Allowed and vibrationally induced transitions are both described. In this pilot implementation, the required geometrical derivatives are calculated by an automated finite-difference method. The scheme is applied to the 1 (1)A"<--1 (1)A' transition of monofluorosilylene (HSiF) and the vibrationally induced 1 (1)A(2)<--1 (1)A(1) transition of water. (C) 2002 American Institute of Physics.
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| 7. |
- Jonsson, D., et al.
(författare)
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Electric and magnetic properties of fullerenes
- 1998
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 109:2, s. 572-577
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Tidskriftsartikel (refereegranskat)abstract
- We present fully analytical ab initio calculations of the electric polarizability, the second hyperpolarizability, and the magnetizability of the fullerenes C 70 and C 84 at the self-consistent field level of theory using large basis sets and - in the case of the magnetizability - London atomic orbitals in order to obtain gauge-origin independent results. These calculations are the first ab initio studies of such properties for C 70 and C 84, and all results are expected to be of near Hartree-Fock limit quality. By comparison with similar results reported earlier for C 60, valuable insight into the electronic structure of the fullerenes is obtained. © 1998 American Institute of Physics.
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| 8. |
- Norman, Patrick, et al.
(författare)
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Density-functional theory calculations of optical rotatory dispersion in the nonresonant and resonant frequency regions
- 2004
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Ingår i: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 120:11, s. 5027-5035
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Tidskriftsartikel (refereegranskat)abstract
- The complex linear response function is extended to mixed electric-dipole-magnetic-dipole properties using London atomic orbitals which ensures gauge-origin independent properties. The optical rotation is determined by mixed electric-dipole-magnetic-dipole polarizability. The anomalous optical rotatory dispersion (ORD) spectra of chiral molecules is calculated using first-principle quantum-chemical methods when absorption is considered. This methodology of ORD is applied to hydrogen peroxide, 3R-methylcyclohexanone, 4R-1,1-dimethyl-[3]-(1,2)-ferrocenophan-2-on, and D2 isomer of C 84 fullerene.
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| 9. |
- Norman, P., et al.
(författare)
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Efficient parallel implementation of response theory : Calculations of the second hyperpolarizability of polyacenes
- 1996
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Ingår i: Chemical Physics Letters. - 0009-2614 .- 1873-4448. ; 253:1-2, s. 1-7
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Tidskriftsartikel (refereegranskat)abstract
- We describe an efficient parallel implementation of response theory for calculations of molecular properties, and demonstrate its performance by calculations on a series of polyacene molecules, from benzene to hexacene. The polarizability and the second hyperpolarizability of the molecules in this series are found to scale as N 1.4 and N 3.5, respectively, where N is the number of benzene rings in the molecule. These N-dependences are weaker than those predicted for the linear polyenes.
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| 10. |
- Paterson, M. J., et al.
(författare)
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Benchmarking two-photon absorption with CC3 quadratic response theory, and comparison with density-functional response theory
- 2006
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 124:5, s. 425-430
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Tidskriftsartikel (refereegranskat)abstract
- We present a detailed study of the effects of electron correlation on two-photon absorption calculated by coupled cluster quadratic response theory. The hierarchy of coupled cluster models CCS, CC2, CCSD, and CC3 has been used to investigate the effects of electron correlation on the two-photon absorption cross sections of formaldehyde (CH2O), diacetylene (C4H2), and water (H2O). In particular, the effects of triple excitations on two-photon transition cross sections are determined for the first time. In addition, we present a detailed comparison of the coupled cluster results with those obtained from Hartree-Fock and density-functional response theories. We have investigated the local-density approximation, the pure Becke-Lee-Yang-Parr (BLYP) functional, the hybrid Becke-3-parameter-Lee-Yang-Parr (B3LYP), and the Coulomb-attenuated B3LYP (CAM-B3LYP) functionals. Our results show that the CAM-B3LYP functional, when used in conjuction with a one-particle basis-set containing diffuse functions, has much promise; however, care must still be exercised for diffuse Rydberg-type states.
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