| 1. |
- 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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| 2. |
- 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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| 3. |
- Rizzo, A., et al.
(författare)
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Sternheimer shieldings and EFG polarizabilities : a density-functional theory study
- 2003
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 372:04-mar, s. 377-385
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Tidskriftsartikel (refereegranskat)abstract
- The electric field gradient (EFG) at the nucleus, the generalized Sternheimer shielding constants, and the EFG hyperpolarizabilities of a set of reference molecules are computed using analytic density-functional (up to quadratic) response theory. At the three-parameter Becke-Lee-Yang-Parr (B3LYP) level, density functional theory (DFT) underestimates correlation effects compared with other approaches such as coupled-cluster and multiconfigurational self-consistent field. For the prediction of EFG properties of hydrogen nuclei and electron-rich atoms such as halides, DFT/ B3LYP provides results even less reliable than Hartree-Fock theory.
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| 4. |
- Salek, Pawel, et al.
(författare)
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Calculations of two-photon absorption cross sections by means of density-functional theory
- 2003
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Ingår i: Chemical Physics Letters. - 0009-2614 .- 1873-4448. ; 374:06-maj, s. 446-452
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Tidskriftsartikel (refereegranskat)abstract
- We present density-functional theory and calculations for two-photon absorption spectra of molecules. The two-photon absorption cross sections are defined in terms of the single residues of the quadratic response function, which was recently derived for density-functional theory using the time-dependent variation principle and the quasi-energy ansatz. The cross-section dependence on different functionals, including the general gradient approximation and hybrid theory, is examined for a set of small molecules. The results of hybrid density-functional theory compare favorably with those from singles-and-doubles coupled-cluster response calculations.
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| 5. |
- Salek, Pawel, et al.
(författare)
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Density-functional theory of linear and nonlinear time-dependent molecular properties
- 2002
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 117:21, s. 9630-9645
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Tidskriftsartikel (refereegranskat)abstract
- We present density-functional theory for linear and nonlinear response functions using an explicit exponential parametrization of the density operator. The response functions are derived using two alternative variation principles, namely, the Ehrenfest principle and the quasienergy principle, giving different but numerically equivalent formulas. We present, for the first time, calculations of dynamical hyperpolarizabilities for hybrid functionals including exchange-correlation functionals at the general gradient-approximation level and fractional exact Hartree-Fock exchange. Sample calculations are presented of the first hyperpolarizability of the para-nitroaniline molecule and of a porphyrin derived push-pull molecule, showing good agreement with available experimental data.
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| 6. |
- Thogersen, L., et al.
(författare)
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The trust-region self-consistent field method : Towards a black-box optimization in Hartree-Fock and Kohn-Sham theories
- 2004
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 121:1, s. 16-27
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Tidskriftsartikel (refereegranskat)abstract
- The trust-region self-consistent field (TRSCF) method is presented for optimizing the total energy E-SCF of Hartree-Fock theory and Kohn-Sham density-functional theory. In the TRSCF method, both the Fock/Kohn-Sham matrix diagonalization step to obtain a new density matrix and the step to determine the optimal density matrix in the subspace of the density matrices of the preceding diagonalization steps have been improved. The improvements follow from the recognition that local models to E-SCF may be introduced by carrying out a Taylor expansion of the energy about the current density matrix. At the point of expansion, the local models have the same gradient as E-SCF but only an approximate Hessian. The local models are therefore valid only in a restricted region-the trust region-and steps can only be taken with confidence within this region. By restricting the steps of the TRSCF model to be inside the trust region, a monotonic and significant reduction of the total energy is ensured in each iteration of the TRSCF method. Examples are given where the TRSCF method converges monotonically and smoothly, but where the standard DIIS method diverges.
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| 7. |
- Tunell, I, et al.
(författare)
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Density functional theory of nonlinear triplet response properties with applications to phosphorescence
- 2003
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 119:21, s. 11024-11034
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Tidskriftsartikel (refereegranskat)abstract
- We present density functional response theory generalized to triplet excitations. A method based on an exponential parametrization of the spin-dependent density operator is derived for the evaluation of linear and quadratic response functions for spin-dependent perturbations. The developed methodology is applicable to commonly available functionals, also hybrid functionals including exchange-correlation functionals at the general gradient-approximation level and fractional exact Hartree-Fock exchange. Illustrative calculations are presented for singlet-triplet transition moments and phosphorescence lifetimes, providing numerical data on these quantities for the first time using time-dependent density functional theory.
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| 8. |
- Watson, M. A., et al.
(författare)
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Linear-scaling formation of Kohn-Sham Hamiltonian : Application to the calculation of excitation energies and polarizabilities of large molecular systems
- 2004
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 121:7, s. 2915-2931
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Tidskriftsartikel (refereegranskat)abstract
- We present calculations of excitation energies and polarizabilities in large molecular systems at the local-density and generalized-gradient approximation levels of density-functional theory (DFT). Our results are obtained using a linear-scaling DFT implementation in the program system DALTON for the formation of the Kohn-Sham Hamiltonian. For the Coulomb contribution, we introduce a modification of the fast multipole method to calculations over Gaussian charge distributions. It affords a simpler implementation than the original continuous fast multipole method by partitioning the electrostatic Coulomb interactions into classical and nonclassical terms which are explicitly evaluated by linear-scaling multipole techniques and a modified two-electron integral code, respectively. As an illustration of the code, we have studied the singlet and triplet excitation energies as well as the static and dynamic polarizabilities of polyethylenes, polyenes, polyynes, and graphite sheets with an emphasis on the trends observed with system size.
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| 9. |
- Watson, M. A., et al.
(författare)
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The calculation of indirect nuclear spin-spin coupling constants in large molecules
- 2004
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 10:18, s. 4627-4639
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Tidskriftsartikel (refereegranskat)abstract
- We present calculations of indirect nuclear spin-spin coupling constants in large molecular systems, performed using density functional theory. Such calculations, which have become possible because of the use of linear-scaling techniques in the evaluation of the Coulomb and exchange-correlation contributions to the electronic energy, allow us to study indirect spin-spin couplings in molecules of biological interest, without having to construct artificial model systems. In addition to presenting a statistical analysis of the large number of short-range coupling constants in large molecular systems, we analyse the asymptotic dependence of the indirect nuclear spin-spin coupling constants on the internuclear separation. In particular, we demonstrate that, in a sufficiently large one-electron basis set, the indirect spin-spin coupling constants become proportional to the inverse cube of the internuclear separation, even though the diamagnetic and paramagnetic spin-orbit contributions to the spin-spin coupling constants separately decay as the inverse square of this separation. By contrast, the triplet Fermi contact and spin-dipole contributions to the indirect spin-spin coupling constants decay exponentially and as the inverse cube of the internuclear separation, respectively. Thus, whereas short-range indirect spin-spin coupling constants are usually dominated by the Fermi contact contribution, long-range coupling constants are always dominated by the negative diamagnetic spin-orbit contribution and by the positive paramagnetic spin-orbit contribution, with small spin-dipole and negligible Fermi contact contributions.
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