Efficient and Accurate Fully Relativistic Density Functional Treatment for Molecules and Periodic Solids*

A fully relativistic density functional method (called quasi-four-component algorithm, Q4C) in combination with numeric atom-centered orbital (NAO) basis functions is presented. Q4C initially projects the atomic solution to (electron-only) positive-energy states and deals with only two components but restores the negative-energy component in a second step; it therefore retains the full precision of traditional four-component relativistic methods. While Q4C inherently reduces the dimension of the Hamiltonian matrix and correspondingly the computational demand in matrix diagonalization, the adoption of localized NAO basis functions further reduces the computational demand in real space operations, enabling us to explore large and complex systems containing heavy elements fully relativistically. Here, we report benchmarks for the properties of a series of common periodic materials and molecules. Additionally, the band structure of a much larger system, i.e. the 2D hybrid organic-inorganic perovskite (2D-HOIP) (4-FPEA)2PbI4 (containing 94 atoms per unit cell) is reported, showing the code's applicability to large systems.

References:
1. J. Chem. Phys., 144, 044105 (2016).
2. Comput. Phys. Commun., 180, 2175 (2009).