Event Title

Single Determinant Excited State Methods: MOM, IMOM, ΔSCF, DIIS

Research Mentor(s)

Tim Kowalczyk

Description

Self-consistent field (SCF) calculations are a MO relaxation technique that iteratively reconstructs an approximated Hamiltonian until the Schrödinger equation converges at an energy minimum, the lowest corresponding to the ground state. Population of the SCF MO’s follows the Aufbau protocol whereby the lowest energy MO’s are filled first, therefore convergence at the ground state is achieved by iterative energy minimization. To converge an SCF calculation at a local minimum corresponding to an excited state is impossible under these MO population rules, therefore the maximum overlap method (MOM) was proposed that populates the new MO’s according to those that have the largest projection onto the span of the previously occupied space. Applying MOM orbital population rules allows convergence of the Hamiltonian to an optimized electron configuration in which a normally virtual orbital becomes occupied, thereby relaxing the excited state for such situations as charge-transfer states (among others). MOM has been further improved to populate orbitals according to their similarity to the initial non-relaxed state, a method called initial maximum overlap method (IMOM) which is useful in systems with near-degeneracies (i.e. a small HOMO-LUMO gap) where the MOM SCF calculations could converge to an undesired state. Benchmarking of this method is reported upon in scientific journals and an original proof of concept illustration was performed in our lab. This poster will seek to illustrate the current single-determinant excited-state method climate by reporting on advancements in the field from within this research group and in the literature. Further work optimizing SCF convergence efficiency with the direct inversion of the iterative subspace (DIIS) method, and application of the Zeigler sum rule to solutions to SCF calculations that purify the spin of the resulting MOs may also be reported on.

Document Type

Event

Start Date

May 2018

End Date

May 2018

Department

Chemistry

Rights

Copying of this document in whole or in part is allowable only for scholarly purposes. It is understood, however, that any copying or publication of this document for commercial purposes, or for financial gain, shall not be allowed without the author’s written permission.

Language

English

Format

application/pdf

This document is currently not available here.

Share

COinS
 
May 17th, 9:00 AM May 17th, 12:00 PM

Single Determinant Excited State Methods: MOM, IMOM, ΔSCF, DIIS

Self-consistent field (SCF) calculations are a MO relaxation technique that iteratively reconstructs an approximated Hamiltonian until the Schrödinger equation converges at an energy minimum, the lowest corresponding to the ground state. Population of the SCF MO’s follows the Aufbau protocol whereby the lowest energy MO’s are filled first, therefore convergence at the ground state is achieved by iterative energy minimization. To converge an SCF calculation at a local minimum corresponding to an excited state is impossible under these MO population rules, therefore the maximum overlap method (MOM) was proposed that populates the new MO’s according to those that have the largest projection onto the span of the previously occupied space. Applying MOM orbital population rules allows convergence of the Hamiltonian to an optimized electron configuration in which a normally virtual orbital becomes occupied, thereby relaxing the excited state for such situations as charge-transfer states (among others). MOM has been further improved to populate orbitals according to their similarity to the initial non-relaxed state, a method called initial maximum overlap method (IMOM) which is useful in systems with near-degeneracies (i.e. a small HOMO-LUMO gap) where the MOM SCF calculations could converge to an undesired state. Benchmarking of this method is reported upon in scientific journals and an original proof of concept illustration was performed in our lab. This poster will seek to illustrate the current single-determinant excited-state method climate by reporting on advancements in the field from within this research group and in the literature. Further work optimizing SCF convergence efficiency with the direct inversion of the iterative subspace (DIIS) method, and application of the Zeigler sum rule to solutions to SCF calculations that purify the spin of the resulting MOs may also be reported on.