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Accurate prediction of K-edge excitation energies using state-specific self-consistent perturbation theory

Lan Nguyen Tran

Abstract

We present the application of the recently developed one-body Møller--Plesset perturbation theory (OBMP2) to the prediction of K-edge excited states. OBMP2 is a self-consistent perturbation theory in which a canonical transformation followed by a cumulant approximation yields an effective one-body Hamiltonian. This resulting operator augments the standard Fock operator with a one-body correlation potential containing double-excitation MP2 amplitudes, allowing molecular orbitals and orbital energies to be optimized in the presence of correlation. This self-consistent framework mitigates convergence and accuracy issues often encountered in standard non-iterative MP2 for open-shell systems and bond-stretching regimes. In this work, we evaluate the performance of an OBMP2-based approach for the calculation of K-edge excitations. Utilizing benchmark test sets of both closed-shell and open-shell molecules, we demonstrate that our method outperforms established standard techniques, including $Δ$DFT, EOM-CCSD, and USTEOM-CCSD. Our findings establish the OBMP2-based $Δ$SCF protocol as a robust and accurate new computational method for the treatment of K-edge excited states.

Accurate prediction of K-edge excitation energies using state-specific self-consistent perturbation theory

Abstract

We present the application of the recently developed one-body Møller--Plesset perturbation theory (OBMP2) to the prediction of K-edge excited states. OBMP2 is a self-consistent perturbation theory in which a canonical transformation followed by a cumulant approximation yields an effective one-body Hamiltonian. This resulting operator augments the standard Fock operator with a one-body correlation potential containing double-excitation MP2 amplitudes, allowing molecular orbitals and orbital energies to be optimized in the presence of correlation. This self-consistent framework mitigates convergence and accuracy issues often encountered in standard non-iterative MP2 for open-shell systems and bond-stretching regimes. In this work, we evaluate the performance of an OBMP2-based approach for the calculation of K-edge excitations. Utilizing benchmark test sets of both closed-shell and open-shell molecules, we demonstrate that our method outperforms established standard techniques, including DFT, EOM-CCSD, and USTEOM-CCSD. Our findings establish the OBMP2-based SCF protocol as a robust and accurate new computational method for the treatment of K-edge excited states.
Paper Structure (4 sections, 9 equations, 3 figures, 2 tables)

This paper contains 4 sections, 9 equations, 3 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Review of OBMP2 theory
  3. Results and discussion
  4. Conclusion

Figures (3)

  • Figure 1: Errors relative to experiment of K-edge excitation energies from $\Delta$HF, $\Delta$OBMP2, and $\Delta$PBE0 for the C center in four molecules.
  • Figure 2: MAEs and RMSEs relative to experiment for different K-edge transition given in Table \ref{['tab:closed-shell']}.
  • Figure 3: MAEs and RMSEs relative to experiment for different K-edge transition given in Table \ref{['tab:open-shell']}.