An approach to study the relativistic effects of large systems with some parts containing heavy elements

The method joining 2-component and scalar relativistic density functional calculations is introduced to simplify the electronic structure calculations of large molecules with some parts containing heavy elements. It is based on the relativistic ZORA density functional method with the atomic potential approximation. The validity of the method is examined through calculations of several molecules containing heavy elements. The calculated molecular total energies, energies of decomposition reactions and electron population on constituent atoms by the method joining 2-component and scalar density functional calculations are in excellent accordance with those from normal 2-component relativistic density functional calculations for the corresponding molecules. The deviation is so small that replacing the latter with the former would not lower the calculation accuracy to a sensible extent for the density functional calculations based on the existent approximate density functionals. Thus the method joining 2-component and scalar relativistic density functional calculations can be used in most theoretical studies by means of density functional theory with relativistic effects taken into account. The method can be implemented with ease and is flexible in use. It may be an attractive approach for the theoretical study of large systems with some parts containing heavy elements.