A non-linear approach to configuration interaction: The low-rank CI method (LR CI)

Olsen, Jeppe (författare)

Malmqvist, Per-Åke (författare)

Roos, Björn O (författare)

Lindh, Roland, 1958- (författare): Department of Theoretical Chemistry, Lund University

Widmark, Per-Olof (författare)

(creator_code:org_t)

Elsevier BV, 1987
1987
Engelska.
Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 133:2, s. 91-101

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Abstract Ämnesord

Stäng

An alternative to the linear CI expansion is presented, which is based on the spectral resolution of the double excitation CI coefficients arranged as a symmetric matrix. The resulting energy expression is a quartic function of the new variables, where the double excitation operator is given as T̂2 = ∑IMωI(d̂I)2, where d̂dI is a single excitation operator: d̂I =∑Ia,d̂IiaÊai. Since M is a small number, the number of variables is reduced considerably compared to normal SDCI, with only little loss in accuracy. A program for non-linear CI calculations has been written and is presented with results for H2O and N2. The method can easily be extended to include orbital optimization and cluster terms in the wavefunction, still yielding a fully variational approximation to the Schrödinger equation.

Av författaren/redakt...: Olsen, Jeppe; Malmqvist, Per-Å ...; Roos, Björn O; Lindh, Roland, 1 ...; Widmark, Per-Olo ...

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