Generalized spin σ-SCF method

doi:10.1063/5.0178264

Return

Generalized spin σ-SCF method

2023-12-04

Ofelia B. Oña

Gustavo E. Massaccesi

DOI：10.1063/5.0178264

Original

Original request for help

Save

Abstract

En 中文

We introduce a generalization of the sigma-SCF method to approximate noncollinear spin ground and excited single-reference electronic states by minimizing the Hamiltonian variance. The new method is based on the sigma-SCF method, originally proposed by Ye et al. [J. Chem. Phys. 147, 214104 (2017)], and provides a prescription to determine ground and excited noncollinear spin states on an equal footing. Our implementation was carried out utilizing an initial simulated annealing stage followed by a mean-field iterative self-consistent approach to simplify the cumbersome search introduced by generalizing the spin degrees of freedom. The simulated annealing stage ensures a broad exploration of the Hilbert space spanned by the generalized spin single-reference states with random complex element-wise rotations of the generalized density matrix elements in the simulated annealing stage. The mean-field iterative self-consistent stage employs an effective Fockian derived from the variance, which is utilized to converge tightly to the solutions. This process helps us to easily find complex spin structures, avoiding manipulating the initial guess. As proof-of-concept tests, we present results for H-n (n = 3-7) planar rings and polyhedral clusters with geometrical spin frustration. We show that most of these systems have noncollinear spin excited states that can be interpreted in terms of geometric spin frustration. These states are not directly targeted by energy minimization methods, which are meant to converge to the ground state. This stresses the capability of the sigma-SCF methodology to find approximate noncollinear spin structures as mean-field excited states.

Keywords:

MOLECULAR SCHRODINGER-EQUATION

DENSITY-FUNCTIONAL THEORY

LOCAL-ENERGY METHOD

EXCITED-STATES

CONFIGURATION-INTERACTION

ELECTRONIC-ENERGY

WAVE-FUNCTIONS

GROUND-STATE

SYMMETRY

MATRIX