Analytic First-Order Derivatives of CASPT2 with IPEA shift

17 February 2023, Version 1
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

Complete active space second-order perturbation theory (CASPT2) is useful for accurately predicting properties of complex electronic structures, but it is well known that it systematically underestimates excitation energies. The underestimation can be corrected using the ionization potential--electron affinity (IPEA) shift. In this study, analytic first-order derivatives of CASPT2 with IPEA shift are developed. CASPT2-IPEA is not invariant with respect to rotations among active molecular orbitals, and two additional constraint conditions are necessary in the CASPT2 Lagrangian to formulate analytic derivatives. The method developed here is applied to methylpyrimidine derivatives and cytosine, and minimum energy structures and conical intersections are located. By comparing energies relative to the closed-shell ground state, we find that the agreement with experiments and high-level calculations is indeed improved by inclusion of the IPEA shift. The agreement of geometrical parameters with high-level calculations may also be improved in some cases.

Supplementary materials

Title
Description
Actions
Title
Supplementary Material: Analytic First-Order Derivatives of CASPT2 with IPEA Shift
Description
Supplementary Material
Actions

Comments

Comments are not moderated before they are posted, but they can be removed by the site moderators if they are found to be in contravention of our Commenting Policy [opens in a new tab] - please read this policy before you post. Comments should be used for scholarly discussion of the content in question. You can find more information about how to use the commenting feature here [opens in a new tab] .
This site is protected by reCAPTCHA and the Google Privacy Policy [opens in a new tab] and Terms of Service [opens in a new tab] apply.