Large unit cells and metallic slabs
Posted: Tue May 26, 2015 6:57 pm
The calculation of the ground state in an elongated unit cell is challenging due to the phenomenon of charge sloshing during SCF iterations. This problem is made more acute if the cell contains a metallic object, such as a periodic slab representing a metallic surface. Using the default parameters to compute the ground state may not lead to convergence. The parameters controlling charge mixing between SCF iterations (charge_mix_coeff, charge_mix_ndim, charge_mix_rcut) can be adjusted to remedy the problem. The ground state calculation can also be started using the -atomic_density option in the run command. The following example shows how to compute the electronic ground state for a 64-atom Pd slab immersed in 64 water molecules, in a unit cell of size (20.79740 x 18.0111 x 50.7358):
Code: Select all
s2ws.sys
set ecut 85
set nempty 128
set fermi_temp 2000
set xc PBE
set wf_dyn PSD
randomize_wf
set charge_mix_rcut 7
set charge_mix_ndim 10
set scf_tol 1.e-6
run -atomic_density 0 100 20