How to adjust the densities at different temperatures during MD

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fanghz · #1 Post by **fanghz** » Thu May 31, 2007 2:50 pm

Dear sir,
I am performing ab-initial molecular dynamics with SMASS=-1 . First, I run the system for 1000 MD steps at a fixed temperature (for example,TEBEG=TEEND=2600K). Then I quench the system from 2600K to 300K. Finnally I run the system for 1000 MD steps at 300K. For the temperature 2600K and 300K respectively, the density of the system should be different, and I want to know whether there is certain criterion to adjust the density of the system (that is to change the length of lattice vector in POSCAR file). I found there is a large value (-200kbar) for the "external pressure" in the OUTCAR file at 2600K using the solid metal density. Should the external pressure be adjusted to equal to "zero" by change the length of lattice vector ? Can vasp calculate the liquid metal density ? I have found the external pressure was influenced by the cell volume, the parameter PREC, ENCUT and the kind of POTCAR (US,PAW). My INCAR file is as follow:

SYSTEM = zr_md

PREC = Low
IALGO = 48
LREAL = A
NELMIN = 4
BMIX = 2.0
MAXMIX = 50

ISIF =2
IBRION = 0
ISYM = 0
NSW = 1000
NBLOCK = 1 ; KBLOCK = 100
SMASS = -1
POTIM = 5
TEBEG = 2600
TEEND = 2600

LWAVE = .FALSE.
LCHARG = .FALSE.
PSTRESS =0

#2 Post by **admin** » Fri Jun 01, 2007 1:13 pm

There is no possibility to vary V in an MD run.

fanghz · #3 Post by **fanghz** » Sat Jun 02, 2007 10:39 am

I mean can I adjust the V manually at constant T ? Many literatures mentioned the V could be adjusted by "zero pressure method" manually ? Does "zero pressure method" mean to make the ''external pressure" in the OUTCAR to be zero ?

#4 Post by **admin** » Fri Jun 15, 2007 11:18 am

as I said, this is not possible. Keeping zero pressure automatically implies an automatic relaxation of the cell volume.