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I found the elastic constants and bulk modules of diamond is wrong by a VASP job


the input files below

==========================
SYSTEM = Di
ICHARG = 2
ENCUT = 700
ISMEAR = -5
IBRION = 6
NSW = 10111
ISIF = 4
EDIFF = 0.00000001
NFREE = 2
LCHARG = F
LWAVE = F
POTIM = 0.015

=================================

K
0
M
15 15 15
0 0 0
=============================





here are some outputs:
===================================

TOTAL ELASTIC MODULI (kBar)
Direction XX YY ZZ XY YZ ZX
--------------------------------------------------------------------------------
XX 11070.1035 1500.6893 1500.6893 0.0000 0.0000 0.0000
YY 1500.6893 11070.1035 1500.6893 0.0000 0.0000 0.0000
ZZ 1500.6893 1500.6893 11070.1035 0.0000 0.0000 0.0000
XY 0.0000 0.0000 0.0000 5911.9935 0.0000 0.0000
YZ 0.0000 0.0000 0.0000 0.0000 5911.9935 0.0000
ZX 0.0000 0.0000 0.0000 0.0000 0.0000 5911.9935
--------------------------------------------------------------------------------



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LATTYP: Found a simple cubic cell.
ALAT = 3.5329679502

Lattice vectors:

A1 = ( 3.5329679502, 0.0000000000, 0.0000000000)
A2 = ( 0.0000000000, 3.5329679502, 0.0000000000)
A3 = ( 0.0000000000, 0.0000000000, 3.5329679502)
Subroutine PRICEL returns following result:

LATTYP: Found a face centered cubic cell.
ALAT = 3.5329679502

Lattice vectors:

A1 = ( 1.7664839751, 1.7664839751, 0.0000000000)
A2 = ( 1.7664839751, 0.0000000000, -1.7664839751)
A3 = ( 0.0000000000, 1.7664839751, -1.7664839751)

4 primitive cells build up your supercell.
========================================



<span class='smallblacktext'>[ Edited ]</span>

btw: the bulk modules of diamond by the vasp results is >700Gpa, it should be under 500

which potential did you use,
how large was the remaining external pressure on the unit cell,
which procedure did you use to determine the bulk lattice constant of your cell?
which convergence criterium did you set for the remaining forces/stress tensors