| 1. |
- Aidas, Kestutis, et al.
(författare)
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The Dalton quantum chemistry program system
- 2014
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Ingår i: Wiley Interdisciplinary Reviews. Computational Molecular Science. - : Wiley. - 1759-0876. ; 4:3, s. 269-284
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Tidskriftsartikel (refereegranskat)abstract
- Dalton is a powerful general-purpose program system for the study of molecular electronic structure at the Hartree-Fock, Kohn-Sham, multiconfigurational self-consistent-field, MOller-Plesset, configuration-interaction, and coupled-cluster levels of theory. Apart from the total energy, a wide variety of molecular properties may be calculated using these electronic-structure models. Molecular gradients and Hessians are available for geometry optimizations, molecular dynamics, and vibrational studies, whereas magnetic resonance and optical activity can be studied in a gauge-origin-invariant manner. Frequency-dependent molecular properties can be calculated using linear, quadratic, and cubic response theory. A large number of singlet and triplet perturbation operators are available for the study of one-, two-, and three-photon processes. Environmental effects may be included using various dielectric-medium and quantum-mechanics/molecular-mechanics models. Large molecules may be studied using linear-scaling and massively parallel algorithms. Dalton is distributed at no cost from for a number of UNIX platforms.
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| 2. |
- Coriani, Sonia, et al.
(författare)
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Linear-scaling implementation of molecular response theory in self-consistent field electronic-structure theory
- 2007
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 126:15, s. 11930-11935
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Tidskriftsartikel (refereegranskat)abstract
- A linear-scaling implementation of Hartree-Fock and Kohn-Sham self-consistent field theories for the calculation of frequency-dependent molecular response properties and excitation energies is presented, based on a nonredundant exponential parametrization of the one-electron density matrix in the atomic-orbital basis, avoiding the use of canonical orbitals. The response equations are solved iteratively, by an atomic-orbital subspace method equivalent to that of molecular-orbital theory. Important features of the subspace method are the use of paired trial vectors (to preserve the algebraic structure of the response equations), a nondiagonal preconditioner (for rapid convergence), and the generation of good initial guesses (for robust solution). As a result, the performance of the iterative method is the same as in canonical molecular-orbital theory, with five to ten iterations needed for convergence. As in traditional direct Hartree-Fock and Kohn-Sham theories, the calculations are dominated by the construction of the effective Fock/Kohn-Sham matrix, once in each iteration. Linear complexity is achieved by using sparse-matrix algebra, as illustrated in calculations of excitation energies and frequency-dependent polarizabilities of polyalanine peptides containing up to 1400 atoms.
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| 3. |
- Cronstrand, P., et al.
(författare)
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Density functional response theory calculations of three-photon absorption
- 2004
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 121:19, s. 9239-9246
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Tidskriftsartikel (refereegranskat)abstract
- Three-photon absorption probabilities delta(3PA) have been calculated through application of a recently derived method for cubic response functions within density functional theory (DFT). Calculations are compared with Hartree-Fock (HF) and with a coupled cluster hierarchy of models in a benchmarking procedure. Except for cases having intermediate states near resonance, density functional theory is demonstrated to be in sufficient agreement with the highly correlated methods in order to qualify for predictions of delta(3PA). For the larger systems addressed, a set of acceptor A and donor D substituted pi-conjugated systems formed by trans-stilbene and dithienothiophene (DTT), we find noticeable differences in the magnitude of delta(3PA) between HF and DFT, although similar trends are followed. It is shown that the dipolar structures, TS-AD and DTT-AD, have substantially larger delta(3PA) than other types of modifications which is in accordance with observations for two-photon absorption. This is the first application of density functional theory to three-photon absorption beyond the use of few-state models.
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| 4. |
- Helgaker, Trygve, et al.
(författare)
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Self-consistent field methods applied to large molecular systems
- 2006
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Ingår i: RECENT PROGRESS IN COMPUTATIONAL SCIENCES AND ENGINEERING, VOLS 7A AND 7B. - : VSP BV-C/O BRILL ACAD PUBL. - 9789004155428 ; , s. 1297-1297
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Konferensbidrag (refereegranskat)abstract
- With recent developments in theory and in implementation, Hartree-Fock and density-functional theory (DFT) self-consistent field (SCF) methods can now be applied to large molecular systems, at a cost that scales linearly with system size. In the present talk, such developments are reviewed, with emphasis on the calculation of energy and molecular properties. In particular, it is demonstrated that energies and molecular properties can now be determined entirely in the atomic orbital (AD) basis, with no implicit or explicit introduction of canonical molecular orbitals in the course of the calculation. After a discussion of energy optimization and convergence of the self-consistent field iterations, some applications are presented, with emphasis on polarizabilities and excitation energies and on the comparison of results obtained by Hartree-Fock and DFT theories in extended systems.
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| 5. |
- Jansik, Branislav, et al.
(författare)
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Ab initio study of the two-photon circular dichroism in chiral natural amino acids
- 2007
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 111:2, s. 446-460
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Tidskriftsartikel (refereegranskat)abstract
- Two-photon circular dichroism spectra calculated within an origin-invariant density functional theory approximation in the absorption region where the lowest electronic excited states appear are presented for all 19 essential amino acids in the gas phase. A comparison of intensities and characteristic features is made with the corresponding two-photon absorption and one-photon circular dichroism spectra for each species. Also, the contributions of the electric dipole, magnetic dipole, and electric quadrupole transitions to the rotational strengths are analyzed in some detail. The remarkable fingerprinting capabilities of the two-photon circular dichroism spectroscopy are highlighted.
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| 6. |
- Jansik, Branislav, et al.
(författare)
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Calculations of static and dynamic polarizabilities of excited states by means of density functional theory
- 2004
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 121:16, s. 7595-7600
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Tidskriftsartikel (refereegranskat)abstract
- We present density functional theory and calculations for excited state second order, static or dynamic, properties. The excited state properties are identified from a double residue of a cubic response function. The performance of various functionals, including the generalized gradient approximation and fractional exact Hartree-Fock exchange, is compared to coupled cluster calculations. Applications on excited state polarizabilities of s-tetrazine and pyrimidine show a good agreement with ab initio correlated, coupled cluster, results.
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| 7. |
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| 8. |
- Jansik, Branislav, et al.
(författare)
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Strong two-photon circular dichroism in helicenes : A theoretical investigation
- 2008
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Ingår i: Journal of Chemical Theory and Computation. - : American Chemical Society (ACS). - 1549-9618 .- 1549-9626. ; 4:3, s. 457-467
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Tidskriftsartikel (refereegranskat)abstract
- Using a recently derived origin-invariant quadratic response approach combined with time-dependent density functional theory, four representative helicenes are shown to present a very strong two-photon circular dichroism (TPCD) response, which makes them candidates for the first experimental observation of a TPCD effect. The large response is attributed to the unique combination of chirality and electron delocalization. Comparison with electronic circular dichroism and two-photon absorption (TPA) shows that the three effects exhibit complementary features for unravelling the molecular structures. In particular, for the four (M)-helicenes studied here, the first, i.e., low-energy, dominant Cotton band is always negative, whereas for TPCD it is positive. From an analysis of the frontier orbitals describing most of the one-electron excitation vectors, the largest TPCD response of tetramethoxy-bisquinone-dithia-[7]-helicene has been attributed to the charge-transfer character of the excited state, like for the parent TPA effect. Moreover, the TPCD intensities are found to be mostly governed by the electric and magnetic dipole contributions, while the electric quadrupole terms are, on a relative basis, less important.
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| 9. |
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| 10. |
- Jonsson, Dan, et al.
(författare)
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Kohn–Sham Time-Dependent Density Functional Theory with Applications to Linear and Nonlinear Properties
- 2006
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Ingår i: Nonlinear optical properties of matter. - Dordrecht : Springer Netherlands. - 9781402048500 ; , s. 151-209
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Bokkapitel (refereegranskat)abstract
- We review Kohn–Sham density-functional theory for time-dependent response functionsup to and including cubic response. The working expressions are derived from anexplicit exponential parametrization of the density operator and the Ehrenfest principle,alternatively the quasi-energy ansatz. While the theory retains the adiabatic approximation,implying that the time-dependency of the functional is obtained only implicitly—through the time-dependency of the density itself rather than through the form ofthe exchange-correlation functionals—our implementation generalizes previous timedependentapproaches in that arbitrary functionals can be chosen for the perturbed densities(energy derivatives or response functions). Thus, the response of the density canalways be obtained using the stated density functional, or optionally different functionalscan be applied for the unperturbed and perturbed densities, even different functionals fordifferent response order. In particular, general density functionals beyond the local densityapproximation can be applied, such as hybrid functionals with exchange–correlation atthe generalized gradient-approximation level and fractional exact Hartree–Fock exchange.We also review some recent progress in time-dependent density functional theory foropen-shell systems, in particular spin-restricted and spin restricted-unrestricted formalismsfor property calculations. We highlight a sample of applications of the theory
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