Getting good convergence in density functional theory codes

Sometimes, getting converged solution to the desired molecule or crystal is painstaking. The solution lies in selecting

1. proper initial guess
2. selection of scf algorithm

for the particular calculation. The commenly used intial guess in gaussian basis set based codes are SAD, CORE, GWH, READ.

In VASP code, the available initial guess is SAD and another one is to READ from CHGCAR file (if available). Another one is reading from the initial wave fuctiontions. In VASP, ICCHARG tag determines the intial guess. It can take values 0 | 1 | 2 |.