Complete active space and corrected density functional theories helping each other to describe vertical electronic π → π* excitations in prototype multiple-bonded molecules

Oleg V Gritsenko; Katarzyna Pernal

doi:10.1063/1.5103220

Complete active space and corrected density functional theories helping each other to describe vertical electronic π → π^* excitations in prototype multiple-bonded molecules

J Chem Phys. 2019 Jul 14;151(2):024111. doi: 10.1063/1.5103220.

Authors

Oleg V Gritsenko¹, Katarzyna Pernal¹

Affiliation

¹ Institute of Physics, Lodz University of Technology, PL-90-924 Lodz, Poland.

PMID: 31301716
DOI: 10.1063/1.5103220

Abstract

The CASΠDFT method, which combines the complete active space (CAS) wave function approach and density functional theory (DFT), offers an efficient description of important excitations to the lowest excited states. CASΠDFT employs a correlation DFT functional corrected with a function P[x] of the ratio xr of the conditional and conventional electron densities obtained with the CAS on-top pair density Π(r). The sectors of P[x] for x(r) ≤ 1 and x(r) > 1 represent the opposite effects of the suppression of dynamic correlation with nondynamic correlation and its enhancement due to the ionic-type excitation. The present combination of the self-consistent-field CAS and the corrected Lee-Yang-Parr correlation functional closely reproduces in the relatively small double-zeta basis the benchmark experimental lowest singlet vertical π → π^* excitations in the prototype multiple-bonded molecules N₂, CO, C₂H₂, and C₂H₄.