Linear response equations revisited: a simple and efficient iterative algorithm

Alessandro, Riccardo;Giannì, Ivan;Pes, Federica;Nottoli, Tommaso

;Lipparini, Filippo

2023-01-01

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Abstract

We present an algorithm to solve the linear response equations for Hartree-Fock, Density Functional Theory, and the Multiconfigurational Self-Consistent Field method that is both simple and efficient. The algorithm makes use of the well-established symmetric and antisymmetric combinations of trial vectors but further orthogonalizes them with respect to the scalar product induced by the response matrix. This leads to a standard, symmetric block eigenvalue problem in the expansion subspace that can be solved by diagonalizing a symmetric, positive definite matrix half the size of the expansion space. Numerical tests showed that the algorithm is robust and stable.