6.15 Memory requirements

 

The memory requirements of VASP can easily exceed your computer facilities. In this case the first step is to estimate where the excessive memory requirements come from. There are two possibilities:

• Storage of wave functions: All bands for all k-points must be kept in memory at the same time. The memory requirements for the wave functions are:

   NKDIM*NBANDS*NRPLWV*16

  The factor 16 arises from the fact that all quantities are COMPLEX*16.
• Work arrays for the representation of the charge density, local potentials, structure factor and large work arrays: A total of approximately 8 arrays is allocated on the second finer grid:

   4*(NGXF/2+1)*NGYF*NGZF*16

  Once again all quantities are COMPLEX*16.

Try to reduce the memory requirements by reducing the corresponding parameters. See section 10 for a discussion on the minimal requirement of these parameters.

For a more accurate calculation of the memory requirements use the following sheet:

minimal alloc (NEDOS=300) 4-10 Mbytes

arrays on large grid ( 5 + NTYP )*MPLWVM*16

arrays on small grid 3.5 *MPLWV *16

wavefunctions (NRPLWV+2*NIOND*LMDIM)*(NBANDS+IADD)*IG

real space projectors IRMAX*(LMDIM+2)*NIOND*8

rotation matrizes 3*NBANDS*NBANDS* IG total

IG=16 for COMPLEX version

IG=8 for gamma point only version

IADD= 2 without residual minimization, 10 with residual minimization

arrays on large grid:
CHTOT, DENCOR, CHTOTL, (CHGGA,CVTOT), CSTRF(NTYPD)
CWORK1, CWORK2

arrays on small grid
CHDEN, CV, CWORK3, CWORK4

wavefunctions
CPTWFP, CPROJ, CPROTM

real space projectors
RPROJ, CRREXP

rotation matrices
CHAM,(COVL,CTMP),CHAMIN

(..,..) means equivalence

In vasp.4.4 the memory requirements can be also calculated by the makeparam utility, which is supplied in the vasp.4.4 directory. It can be created by typing

> make makeparam

in the vasp.4.4 directory.