Localized Active Space State Interaction: A Multireference Method For Chemical Insight

23 May 2022, Version 1
This content is a preprint and has not undergone peer review at the time of posting.


Multireference electronic structure methods, like the complete active space (CAS) selfconsistent field model, have long been used to characterize chemically interesting processes. Important work has been done in recent years to develop modifications having lower computational cost than CAS, but typically these methods offer no more chemical insight than that from the CAS solution being approximated. In this paper, we present the localized active space - state interaction (LASSI) method that can be used not only to lower the intrinsic cost of the multireference calculation, but also to improve interpretability. The localized active space (LAS) approach utilizes the local nature of electron-electron correlation to express a composite wave function as an antisymmetrized product of unentangled wave functions in local active subspaces. LASSI then uses these LAS states as a basis from which to express complete molecular wave functions. This not only makes the molecular wave function more compact, but it also permits flexibility in choosing those states to include in the basis. Such selective inclusion of states translates to selective inclusion of specific types of interactions, thereby allowing a quantitative analysis of these interaction. We demonstrate the use of LASSI to study charge migration and spin-flip excitations in multireference organic molecules. We also compute the J coupling parameter for a bimetallic compound using various LAS bases to construct the Hamiltonian to provide insight into the coupling mechanism.


Multireference Method
Chemical Insight
Localized Active Space
J coupling
Charge migration

Supplementary materials

Supporting information for - Localized Active Space State Interaction: A Multireference Method For Chemical Insight
Absolute electronic energies, and equilibrium molecular geometry Cartesian coordinates are provided.


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.