Extension and acceleration of relativistic density functional theory based on transformed density operator.

Yasuhiro Ikabata,Junji Seino,Hiromi Nakai,Takuro Oyama,Masao Hayami

doi:10.1063/1.5090523

Yasuhiro Ikabata, Junji Seino + Show 3 more

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https://doi.org/10.1063/1.5090523

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Abstract

We report an extension of relativistic density functional theory (RDFT) within one-component or two-component expressions that relies on a unitary-transformed density operator as well as a unitary-transformed Hamiltonian [Oyama et al., Chem. Phys. Lett. 680, 37 (2017)]. The transformed density operator is introduced to avoid the picture-change effect in the electron density, density gradient, kinetic energy density, and exchange-correlation potential. We confirmed that the implementation based on the spin-free infinite-order Douglas-Kroll-Hess method gives total, orbital, and excitation energies close to the reference values given by four-component RDFT calculations. To reduce the computational cost due to the transformed density operator, the local unitary transformation was also implemented. Numerical assessments revealed that the present scheme enabled the RDFT calculation of polyatomic systems with negligibly small picture-change effect.

Highlights

Relativistic density functional theory (RDFT), which is rationalized by the Rajagopal–Callaway theorem,1 has been developed within two frameworks, namely, four-component and twocomponent relativistic density functional theory (RDFT)
We report an extension of relativistic density functional theory (RDFT) within one-component or two-component expressions that relies on a unitary-transformed density operator as well as a unitary-transformed Hamiltonian [Oyama et al, Chem
The formulation focuses on the ground-state calculation with various types of exchange-correlation functionals and the excitation energy obtained by linear-response time-dependent density functional theory (TDDFT)

Summary

Introduction

Relativistic density functional theory (RDFT), which is rationalized by the Rajagopal–Callaway theorem, has been developed within two frameworks, namely, four-component and twocomponent RDFT. In four-component RDFT, the operators and wavefunction consist of two large and two small components. The exchange-correlation energy is a functional of the electron density and current density under a no-pair approximation.. Instead of the current density, RDFT is formulated as a functional of the electron density only or by introducing the spin magnetization vector or spin density.. Relativistic exchange-correlation functionals have been reported, the functionals derived in the nonrelativistic framework are employed in practice. Four-component RDFT sufficiently captures the relativistic effects in chemistry, the large computational cost due to the number of components is problematic in its application to large systems

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