| 1. |
- Choe, Yong-Kee, et al.
(författare)
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Theoretical study of the electronic ground state of iron(II) porphine. II
- 1999
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 111:9, s. 3837-3845
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Tidskriftsartikel (refereegranskat)abstract
- Ten low-lying electronic states of Fe(II) porphine, (5)A(1g), E-5(g), B-5(2g), (3)A(2g), B-3(2g), E-3(g)(A), E-3(g)(B), (1)A(1g), B-1(2g), and E-1(g) states, are studied with multiconfigurational second-order perturbation (CASPT2) calculations with complete active space self-consistent field (CASSCF) reference functions with larger active space and basis sets. The enlargement of active space and basis sets has no influence on the conclusion of a previous multireference Moller-Plesset perturbation (MRMP) study. The present CASPT2 calculation concludes that the (5)A(1g) state is the ground state. A relativistic correction has been performed by the relativistic scheme of eliminating small components (RESC). For energetics, no significant contribution from the relativistic correction was found. The relative energies and orbital energies are not changed appreciably by the introduction of a relativistic correction. The present result does not agree with all the spectroscopic observations, but is consistent with a magnetic moment study.
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| 2. |
- Lindh, Roland, 1958-, et al.
(författare)
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Semidirect parallel self-consistent field : the load balancing problem in the input/output intensive self-consistent field iterations
- 2003
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Ingår i: Theoretical Chemistry accounts. - : Springer Science and Business Media LLC. - 1432-881X .- 1432-2234. ; 110:3, s. 156-164
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Tidskriftsartikel (refereegranskat)abstract
- The full capacity of contemporary parallel computers can, in the context of iterative ab initio procedures like, for example, self-consistent field (SCF) and multiconfigurational SCF, only be utilized if the disk and input/output (I/O) capacity are fully exploited before the implementation turns to an integral direct strategy. In a recent report on parallel semidirect SCF http://www.tc.cornell.edu/er/media/1996/collabrate.html, http://www.fp.mcs.anl.gd/grand-challenges/chem/non-direct/index.html it was demonstrated that super-linear speedups are achievable for algorithms that exploit scalable parallel I/O. In the I/O-intensive SCF iterations of this implementation a static load balancing, however, was employed, dictated by the initial iteration in which integral evaluation dominates the central processing unit activity and thus determines the load balancing. In the present paper we present the first implementation in which load balancing is achieved throughout the whole SCF procedure, i.e. also in subsequent iterations. The improved scalability of our new algorithm is demonstrated in some test calculations, for example, for 63-node calculation a speedup of 104 was observed in the computation of the two-electron integral contribution to the Fock matrix.
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| 3. |
- Nakayama, Kenichi, et al.
(författare)
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Different bases for different correlation effects : multireference Moller-Plesset perturbation theory in the extended basis function space
- 1999
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Ingår i: Chemical Physics Letters. - 0009-2614 .- 1873-4448. ; 300:3-4, s. 303-311
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Tidskriftsartikel (refereegranskat)abstract
- A method to improve virtual orbitals of CASSCF theory has been proposed by expanding the virtual orbital space through the addition of basis functions without disturbing already established CASSCF function space. It is a natural extension of work used in Hartree-Fock calculations. The improved virtual orbitals are then used to estimate the dynamical correlation. That is, a moderate basis set is used in CASSCF to include nondynamical correlation and a sufficiently large basis set is used in multireference Moller-Plesset perturbation theory to estimate the slowly convergent dynamical correlation. The present formalism is tested on the barrier height of the H2CO –> H-2 + CO reaction, singlet-triplet energy separation in CH2 and valence pi-pi* excitation energies in butadiene. Numerical results show that good accuracy can be obtained.
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| 4. |
- Paulovic, Jozef, et al.
(författare)
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Relativistic and correlated calculations on the ground and excited states of ThO
- 2003
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 119:2, s. 798-805
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Tidskriftsartikel (refereegranskat)abstract
- We report on the performance of the third-order Douglas-Kroll ab initio model potential (DK3-AIMP) method-based electron-correlated spin-orbit calculations. Our treatment assumes that the problem can be separated into a spin-free correlation treatment and a spin-orbit calculation. The correlation effects were calculated using the multistate complete active space second-order perturbation method, and the spin-orbit effects were treated by means of the restricted active space state interaction spin-orbit method, where the spin-orbit effects were approximated by the Douglas-Kroll type of atomic mean-field spin-orbit method. We used our method for illustrative calculations on the ground and low-lying electronic states of thorium monoxide. For a proper description of the inner core region in the spin-orbit calculations, an auxiliary spin-orbit basis set was introduced. The DK3-AIMP-based electron-correlated spin-orbit calculations on ThO yield good agreement with corresponding all-electron results and with the available experimental data. This confirms that the DK3-AIMP method can be easily combined with highly accurate correlation treatments and relativistic effects, both of which are vital for studying the actinides. To our knowledge, the literature contains no references to AIMP calculations on the low-lying states of ThO.
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