| 1. |
- Aidas, Kestutis, et al.
(författare)
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The Dalton quantum chemistry program system
- 2014
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Ingår i: WIREs Computational Molecular Science. - : Wiley. - 1759-0876 .- 1759-0884. ; 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. |
- Jansik, B., et al.
(författare)
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A coupled-cluster study of lanthanum trihalide structures
- 2002
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Ingår i: Journal of the Chemical Society. Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1472-7773 .- 1364-5447. ; :24, s. 4603-4606
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Tidskriftsartikel (refereegranskat)abstract
- Coupled-cluster calculations were carried at the CCSD(T)-level in order to determine the structures and vibrational spectra of the lanthanum trihalides LaF3 and LaCl3. Two different approaches were employed to describe scalar relativistic effects; the quasi-relativistic Effective Core Potential approach and the all-electron Douglas-Kroll approach. We find LaF3 to be of pyramidal structure and LaCl3 to be planar. The obtained vibrational frequencies accord well with experimental measurements except for the v(2) mode. This disagreement is attributed to the intrinsic uncertainty of harmonic frequencies of this fluxional mode as extracted from spectra which were obtained at high temperature and for matrix isolated species.
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| 3. |
- Jansik, B., et al.
(författare)
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Relativistic effects on linear and non-linear polarizabilities of the furan homologues
- 2003
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Ingår i: Journal of Molecular Structure. - : Elsevier BV. - 0166-1280. ; 633:03-feb, s. 237-246
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Tidskriftsartikel (refereegranskat)abstract
- First principles calculations including relativistic effects are carried out for dipole moments, polarizabilities, first- and second-order hyperpolarizabilities for the series of furan homologues XC4H4, X = O, S, Se, Te, at three different levels of theory; time-dependent Dirac-Hartree-Fock (DHF), time-dependent Hartree-Fock with a Douglas-Kroll transformed one-component Hamiltonian, and time-dependent Hartree-Fock using effective-core potentials. By comparison with the corresponding non-relativistic results, the influence of relativistic effects on the properties as well as the accuracy of previously reported calculations on these molecules using effective-core potentials for selenium and tellurium can be addressed. The obtained results indicate that relativistic effects can be described with comparable accuracy at all three employed levels, and that non-scalar effects, which are explicitly treated only at the time-dependent DHF level, are of minor importance. Frequency dispersion and relativity are found to be additive at the single-determinant level. We find that relativistic effects cannot make up for the earlier identified mismatch between theory and experiment for the non-linear polarizabilities of the heavier homologues. A Bishop-Kirtman analysis of vibrational effects indicates that the same can be said about these.
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| 4. |
- Jansik, B., et al.
(författare)
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Relativistic effects on linear and non-linear polarizabilities of the furan homologues
- 2003
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Ingår i: Journal of Molecular Structure. - 0166-1280. ; 633:2-3, s. 237-246
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Tidskriftsartikel (refereegranskat)abstract
- First principles calculations including relativistic effects are carried out for dipole moments, polarizabilities, first- and second-order hyperpolarizabilities for the series of furan homologues XC4H 4, X = O, S, Se, Te, at three different levels of theory, time-dependent Dirac-Hartree-Fock (DHF), time-dependent Hartree-Fock with a Douglas-Kroll transformed one-component Hamiltonian, and time-dependent Hartree-Fock using effective-core potentials. By comparison with the corresponding non-relativistic results, the influence of relativistic effects on the properties as well as the accuracy of previously reported calculations on these molecules using effective-core potentials for selenium and tellurium can be addressed. The obtained results indicate that relativistic effects can be described with comparable accuracy at all three employed levels, and that non-scalar effects, which are explicitly treated only at the time-dependent DHF level, are of minor importance. Frequency dispersion and relativity are found to be additive at the single-determinant level. We find that relativistic effects cannot make up for the earlier identified mismatch between theory and experiment for the non-linear polarizabilities of the heavier homologues. A Bishop-Kirtman analysis of vibrational effects indicates that the same can be said about these. © 2003 Elsevier B.V. All rights reserved.
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| 5. |
- Jansik, B., et al.
(författare)
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Relativistic study of vuv radiation properties from Kr-Xe gas mixtures
- 2003
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 67:4
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Tidskriftsartikel (refereegranskat)abstract
- In an effort to obtain a microscopic understanding of the origin of vuv emission from inert heavy-atom gas mixtures we present results from relativistic calculations of the krypton-xenon spectrum in the 68 000 cm(-1) region. Calculations carried out on the interatomic interaction in the ground and in the low-lying spin-orbit excited states [0(-)(P-3(2)), 0(+)(P-3(1)), 1(P-3(1)), 1(P-3(2)), 2(P-3(1))] of the krypton-xenon dimer are presented. The calculations were executed in a two-step procedure in which the CCSD(T) model for the ground state and the CCSD response theory model for the excited states were used to obtain spin-free potential curves in the first step. A perturbational treatment of the spin-orbit interaction within the atomic mean-field approximation was applied in the next step. Large-core quasirelativistic effective core potentials with richly augmented valence basis sets and midbond functions were used. All calculations were corrected for basis set superposition errors by applying the counterpoise method. For all involved states, spin-orbit perturbed potential energy curves were computed and equilibrium geometries, potential well depths, and local extrema were determined. Vibrational analysis and Franck-Condon factors for the ground and 0(+)(P-3(1)),1(P-3(1)) states were also calculated. The geometry dependence of the electronic dipole transition matrix elements between all involved excited states and the ground state was investigated. Excitation energies and potentials were obtained that are in excellent agreement with results based on fitting to experimental data. Out of some earlier disparate experimental assignments of the character of the excited states of the KrXe complex, the present results adhere most closely to the ones presented by Pibel [J. Chem. Phys. 101, 10 242 (1994)]. Analyzed together with the experimental data, the theoretical results provide a clear picture of the organization of exciplex states and of the origin of strong vuv emission from these states that follows from binary collisions of the heavy inert Kr and Xe atoms.
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| 6. |
- Jansik, B., et al.
(författare)
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Size, order, and dimensional relations for silicon cluster polarizabilities
- 2002
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 106:2, s. 395-399
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Tidskriftsartikel (refereegranskat)abstract
- Response theory calculations in the random phase approximation are applied to linear polarizabilities and second hyperpolarizabilities of 1-, 2-, and 3-dimensional hydrogen-terminated silicon clusters. Successive enlargement of the clusters to embody on the order of 50 silicon atoms plus bond-saturating hydrogen atoms allows for extrapolation to bulk values of individual silicon atom contributions in the 1D and 3D cases. Modern effective core potentials are shown to provide excellent approximations to the all-electron values in all cases; errors for both polarizabilities and hyperpolarizabilities are on the order of 1%. The findings indicate considerable time savings in predictions of the electric polarizability properties of elements beyond the first row atoms.
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| 7. |
- Cronstrand, P., et al.
(författare)
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Density functional 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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| 8. |
- Jansik, B., et al.
(författare)
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Cubic response functions in time-dependent density functional theory
- 2005
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 122:5
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Tidskriftsartikel (refereegranskat)abstract
- We present density-functional theory for time-dependent response functions up to and including cubic response. The working expressions are derived from an explicit exponential parametrization of the density operator and the Ehrenfest principle, alternatively, the quasienergy ansatz. While the theory retains the adiabatic approximation, implying that the time-dependency of the functional is obtained only implicitly-through the time dependence of the density itself rather than through the form of the exchange-correlation functionals-it generalizes previous time-dependent implementations in that arbitrary functionals can be chosen for the perturbed densities (energy derivatives or response functions). In particular, general density functionals beyond the local density approximation can be applied, such as hybrid functionals with exchange correlation at the generalized-gradient approximation level and fractional exact Hartree-Fock exchange. With our implementation the response of the density can always be obtained using the stated density functional, or optionally different functionals can be applied for the unperturbed and perturbed densities, even different functionals for different response order. As illustration we explore the use of various combinations of functionals for applications of nonlinear optical hyperpolarizabilities of a few centrosymmetric systems; molecular nitrogen, benzene, and the C-60 fullerene. Considering that vibrational, solvent, and local field factors effects are left out, we find in general that very good experimental agreement can be obtained for the second dynamic hyperpolarizability of these systems. It is shown that a treatment of the response of the density beyond the local density approximation gives a significant effect. The use of different functional combinations are motivated and discussed, and it is concluded that the choice of higher order kernels can be of similar importance as the choice of the potential which governs the Kohn-Sham orbitals.
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| 9. |
- Jansik, B., et al.
(författare)
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Response theory calculations of two-photon circular dichroism
- 2005
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 414:06-apr, s. 461-467
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Tidskriftsartikel (refereegranskat)abstract
- The feasibility of calculations of two-photon circular dichroism (TPA-CD) by means of response theory is demonstrated. The results from sample applications, involving the calculation of residues of appropriate frequency dependent quadratic response functions within a density functional theory model, show that the structural content of TPA-CD spectra is very different from both normal circular dichroism and two-photon absorption, indicating a unique fingerprinting functionality for chiral species. Combined with increased penetrability of the infrared exciting light and the confocal nature of two-photon absorption, this makes TPA-CD a useful tool for biomolecular identification.
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| 10. |
- Rizzo, A., et al.
(författare)
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Density-functional theory study of electric and magnetic properties of hexafluorobenzene in the vapor phase
- 2005
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 122:23
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Tidskriftsartikel (refereegranskat)abstract
- A series of electric and magnetic properties of hexafluorobenzene have been calculated, including the electric dipole polarizability, magnetizability, electric quadrupole moment, and nonlinear mixed electric dipole-magnetic dipole-electric quadrupole hyperpolarizabilities needed to obtain estimates of the Kerr, Cotton-Mouton, Buckingham, Jones, and magnetoelectric birefringences in the vapor phase. Time-dependent density-functional theory was employed for the calculation of linear-, quadratic, and cubic response functions. A number of density functionals have been considered, along with Sadlej's triple-zeta basis set and the augmented correlation-consistent polarized valence double zeta and augmented correlation-consistent polarized valence triple zeta basis sets. Comparisons have been made with experiment where possible. The analysis of results allows for an assessment of the capability of time-dependent density-functional theory for high-order electromagnetic properties of an electron-rich system such as hexafluorobenzene.
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