1.6. Atomic orbital calculation

In this section, I teach how to perform atomic orbital (AO) calculations. AO calculations are more efficient, especially for large systems, but the accuracy of an AO basis depends on the chemical environment and the atomic configuration. To perform self-consistent, DOS or band structure calculations using the AO basis, define the keyword LCAO.status as true. For example, let’s recompute the ground state density of silicon using AO. Copy the following input file and save it to a text file named si_lcao_scf.txt.

info.calculationType = 'self-consistent'
info.savepath = 'results/si_lcao_scf';
atom.element = [1 1]
atom.xyz = 10.25*[0 0 0;0.25 0.25 0.25]
domain.latvec = 10.25*[0.0 0.5 0.5;0.5 0.0 0.5;0.5 0.5 0.0]
domain.lowres = 0.5
element.species = 'si'
element.path = './Si_TM_LDA.mat'
LCAO.status = 1
kpoint.gridn = [4,4,4]

Then pass it to RESCU and execute the program as follows

rescu -i si_lcao_scf.txt;

The calculation is significantly faster. This is because the Kohn-Sham eigenvalue problem is projected onto the (small) AO subspace. Note that forces are not calculated at the end of atomic orbital calculations as Pulay contributions have not been implemented yet. Relaxation and phonon calculations cannot be performed using an AO basis consequently.