DFT calculations

Preparation of VASP input files

Currently, DFT-raMO supports VASP inputs, and the required VASP outputs are the OUTCAR, POSCAR, KPOINTS, and WAVECAR files. Future versions will support abinit (likely to be tested on versions 8.10.3 and 9.10.1), and this will require a WFK output.

A static calculation should be performed with a POSCAR pertaining to the unit cell geometry. The POSCAR file must specify atomic identities after giving cell parameters but before the stoichiometry and direct coordinates. This is not a problem with VASP version 5 or later, but POSCAR files in VASP 4 do not include this information. Ensure this information is in the POSCAR or add it manually. An example is given below, where the atomic identities are given in the line Sc Al.

Al3 Sc1                                 
   1.00000000000000     
     4.1046969868448775    0.0000000000000000    0.0000000000000000
     0.0000000000000000    4.1046969868448775    0.0000000000000000
     0.0000000000000000    0.0000000000000000    4.1046969868448775
Sc Al
   1   3
Direct
  0.0000000000000000  0.0000000000000000  0.0000000000000000
  0.0000000000000000  0.5000000000000000  0.5000000000000000

A Γ-centered k-point mesh (KPOINTS) corresponding to the desired supercell in real space should also be used. For example, if using a 2×2×3 supercell, the k-point grid must also be 2×2×3. The supercell size should be large enough such that atoms do not interact with their translational copies in neighboring supercells. The recommended starting point is to use a supercell approximately 12 Å in length for each axis (assuming cubic, tetragonal, or orthorhombic systems). A larger grid may be used but the user should be aware that significantly more memory will be needed.

Be sure to turn off symmetry (ISYM = -1) and print the WAVECAR.