Nonadiabatic couplings from time-dependent density functional theory: Formulation in the Casida formalism and practical scheme within modified linear response

Abstract

We present an efficient method to compute nonadiabatic couplings (NACs) between the electronically ground and excited states of molecules, within the framework of time-dependent density functional theory (TDDFT) in frequency domain. Based on the comparison of dynamic polarizability formulated both in the many-body wave function form and the Casida formalism, a rigorous expression is established for NACs, which is similar to the calculation of oscillator strength in the Casida formalism. The adiabatic local density approximation (ALDA) gives results in reasonable accuracy as long as the conical intersection (ci) is not approached too closely, while its performance quickly degrades near the ci point. This behavior is consistent with the real-time TDDFT calculation. Through the use of modified linear response theory together with the ground-state-component separation scheme, the performance of ALDA can be greatly improved, not only in the vicinity of ci but also for Rydberg transitions and charge-transfer excitations. Several calculation examples, including the quantization of NACs from the Jahn-Teller effect in the H3 system, have been given to show that TDDFT can efficiently give NACs with an accuracy comparable to that of wave-function-based methods.

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“…Hu and co-workers have further developed the Chernyak-Mukamel approach for computation of first-order nonadiabatic coupling vectors between the ground state and the first excited state [74][75][76]. Send and Furche have shown that the previous result neglects molecular orbitals derivatives [77].…”

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“…As in the NVPT approach based on the completeadiabatic form of the electron-nuclear wave function [19], the first-order perturbation to the electronic wave function represents the effect of the non-adiabatic coupling between the ground and the excited electronic states. Within a fully non-adiabatic approach [59][60][61][62][63][64][65][66][67][68], it would be possible to compute Eq. (32).…”

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“…Nonadiabatic coupling vectors between the ground and any excited states can in principle be computed exactly from LR-TDDFT, [44][45][46][47][48] while couplings between excited states are only approximated in the linear-response formalism. 49 Nevertheless, it has been shown that the adiabatic approximation to LR-TDDFT (which is effectively the only practical option) cannot properly describe couplings between the first excited state and the ground state.…”