Analytic Molecular Hessian Calculations for CC2 and MP2 Combined with the Resolution of Identity Approximation.

摘要: An implementation of analytic second derivatives for the approximate coupled cluster singles and doubles model CC2 second-order Moller-Plesset perturbation theory (MP2) will be presented. The RI approximation two-electron repulsion integrals is used to reduce memory demands, operation count, I/O requirements. During calculation, storage [Formula: see text] quantities (where a measure system size) can completely avoided. It shown that with MP2 method an appropriate scaling harmonic frequencies, especially C-F stretch frequencies are reproduced much better in comparison experiments than B3LYP density functional. Similar advantages observed molecules strong, internal van der Waals interactions. Spin offers additional improvements these cases. has been tested up 81 atoms 684 basis functions.