Advances in Chemical Physics: Ab Initio Methods in Quantum by PDF

ISBN-10: 0470142944

ISBN-13: 9780470142943

ISBN-10: 0471909017

ISBN-13: 9780471909019

The Advances in Chemical Physics sequence presents the chemical physics and actual chemistry fields with a discussion board for serious, authoritative reviews of advances in each quarter of the self-discipline. full of state-of-the-art learn stated in a cohesive demeanour no longer came upon in other places within the literature, each one quantity of the Advances in Chemical Physics sequence serves because the ideal complement to any complicated graduate category dedicated to the examine of chemical physics.

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Extra info for Advances in Chemical Physics: Ab Initio Methods in Quantum Chemistry Part 2, Volume 69

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0000000969 (6) Iter. O001465216(14) - "For details, see Ref. 56; number of CI updates per iteration in parentheses. *Active space: 80-10o. 3n-4n, 16; start with canonical SCF orbitals. 'Active space: 8u-llu, 3n-5n, 16; start with canonical SCF orbitals. dActive space: 80-1 lo, 3 n - h . 26; start with orbitals from 49 140 CSF calculation this size can now be performed routinely. Table VII shows even larger t e s t calculations for the FeO molecule. The longest CASSCF wavefunction optimized to date comprised 230045 Slater determinants (178 910 CSFs).

In terms of the molecular integrals and the coupling coefficients y can be written as ij J The coupling coefficients ( @ I I E i j I @ J )and ( @ I I E i j , k l l @ J in ) principle need only be constructed once if they are stored on a formula tape. In our program this step can be performed by a graphical unitary group approach (GUGA)27. However, for large CASSCF calculations, the formula tape becomes exceedingly long. This limits the length of the configuration expansion which can be handled by this method to about lo4 configurations.

The number of variational parameters in internally contracted MCSCFSCEP wavefunctions rarely exceeds lo5 even if large basis sets and complex reference wavefunctions are employed. In contrast to the number of variational parameters, the number of coupling coefficients depends on the number of reference configurations. and can become very large if CASSCF references are used. The main problem is, therefore, the calculation and storage of the coupling coefficients. It would be very helpful if at least part of them could be recalculated each time they are needed.

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Advances in Chemical Physics: Ab Initio Methods in Quantum Chemistry Part 2, Volume 69


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