Molecular geometries and harmonic frequencies from the parametric two-electron reduced density matrix method with application to the HCN < = > HNC isomerization.
Energies, geometries, and harmonic frequencies of the chemical species in the HCN < = > HNC isomerization including the transition state are computed with the parametric variational two-electron reduced density matrix (2-RDM) method. The parametric 2-RDM method parametrizes the 2-RDM with single- and double-excitation coefficients to be both size-consistent and nearly N-representable [DePrince, A. E., III; Mazziotti, D. A. Phys. Rev. A 2007, 73, 042501.]. With the inclusion of the zero-point energies of both species, the energy of HNC relative to HCN in a polarized valence triple-zeta basis set is 14.2 kcal/mol, which agrees with the experimental value of 14.8 +/- 2 kcal/mol. The present calculations provide the first assessment of the method for computing harmonic frequencies from a molecular geometry optimization. Bond lengths, angles, and harmonic frequencies are also computed for HF, CO, and H2O.
Department of Chemistry and The James Franck Institute, The University of Chicago, Chicago, Illinois 60637, USA.
A Eugene
AE
DePrince
David A
DA
Mazziotti