Optimally Tuned Multiconfigurational Short-Range DFT for Linear Response Properties

TL;DR

This paper introduces a theoretically grounded optimal-tuning scheme for multiconfigurational short-range DFT, improving the accuracy of linear response properties by determining the range-separation parameter from ionization potentials.

Contribution

We develop an optimal-tuning protocol for MC-srDFT based on electron density decay, enabling system-specific parameter selection for better property predictions.

Findings

Optimal tuning improves polarizability calculations.

The method accurately determines the range-separation parameter from ionization potentials.

Enhanced agreement with experimental and high-level theoretical results.

Abstract

Multiconfigurational short-range density functional theory (MC-srDFT) rigorously combines ground state wavefunction theory with DFT. Unlike single-reference range-separated hybrid functionals, MC-srDFT has lacked theoretically grounded protocols for choosing the system-specific range-separation parameter. To address this problem, we introduce an optimal-tuning scheme based on enforcing the correct exponential decay of the electron density. We show that the range-separation parameter can be determined from the ionization potential given by the smallest-magnitude eigenvalue of the Extended Koopmans' Theorem matrix constructed for the model Hamiltonian. We validate this approach for static and dynamic dipole polarizabilities of ground-state molecular systems using MC-srDFT within both full linear response and its extended random phase approximation (ERPA) variant. Optimal tuning substantially improves polarizabilities relative to the commonly used universal $\mu = 0.4\,\mathrm{bohr}^{-1}$ parameter.