How do i find the correct equilibrium volume.

[yuan_liu2]

Dear VASP officer,

I am trying to relax the VOPO4·2H2O layer structure. I firstly used isif=3, PREC=A, and ENCUt=700 to relax the structure. and then I do calculate the isif =4 to get the exact total energy and external pressure. I also wanted to calculate the modulus of structure, and thus changed the scaling factor from 1 to 1.002 and calculated it one more time. However, the total energy of the former one is -162.3399 eV, the external pressure is 0.27 kB, the expanded structure is -162.343 eV and the external pressure is -1.81 kB. I was so confused that the former one should be the closest structure to the equilibrium state cause the pressure is lower than the latter one. But the latter one shows the lower total energy, which means the expanded structure should be more stable.

Do you have any suggestions about my calculations? Thank you in advance. Glad to hear you.
This is my INCAR:
ENCUT=700
ISPIN=2
MAGMOM=2*5 2*5 14*0 8*0
LREAL=AUTO
EDIFF=1e-6
NELM=200
PREC=Accurate
ISMEAR=-5
ISIF=4
NSIM=4
IBRION=2
NSW=200
LMAXMIX=4
AMIX = 0.02
BMIX = 0.0001

LDAU = .TRUE.
LDAUTYPE=2
LDAUL=2 -1 -1 -1
LDAUU=3.25 0 0 0
LDAUJ=0 0 0 0

LCHARG=.False.
LWAVE=.FAlse.

LPLANE=.TRUE.
EDIFFG = -0.01
ALGO = N
LASPH=.TRUE.

This is the POSCAR:
1.000000000000000
6.2910913667107105 -0.0003161417754701 0.1372213628741708
-0.0003526914617383 6.2953748840613963 0.0022558629713200
0.1617771955944119 0.0026652810383648 7.4349443848233303
V P O H
2 2 14 8
Direct
0.0000724779979251 0.4975768409978656 0.2202757068812957
0.5070294610496120 0.9973787506522527 0.3989086430892854
0.0031214097128540 0.9986393858817948 0.3087603811638644
0.5039801495674894 0.4987171815128022 0.3104902321560630
0.5065981123742844 0.6917433992699387 0.4407779046577431
0.8103896472651613 0.9994257419671086 0.4478734125330988
0.5284055421002591 0.9953377352449948 0.1823236076053689
0.9786564072713304 0.4954036082730582 0.4368608641309777
0.2009426923177955 0.9991791577273972 0.4245318630593289
0.5082309186147569 0.3016048012795167 0.4347068059444226
0.0001120803680905 0.1920351821933579 0.1786952530344266
0.3061670347452434 0.4991022890981824 0.1947416576767793
0.6967381778122288 0.5002427739746125 0.1714073706424770
0.9993295500418569 0.8018836077237737 0.1843341689324802
0.4750925787046825 0.4221112831086700 0.8187717636417204
0.0320341780544524 0.9222224364607143 0.8001320469874997
0.4649802431474512 0.0064623847982332 0.7001372661405298
0.0423208293728266 0.5068347821509107 0.9190561231242782
0.5629394903776017 0.4615328327414048 0.9193556197977699
0.5228049017068770 0.5090143601838975 0.7157492566925256
0.9443918366901016 0.9613846877297618 0.6993059276359475
0.9840134058607646 0.0091498708674607 0.9029314524042249
0.4836659022515306 0.1532698985693486 0.7468692911455150
0.3159371084372609 0.9693567274471491 0.7367121185519778
0.0237408988551806 0.6536911516830273 0.8722094622130214
0.1912794993023610 0.4695416264627568 0.8824770071573695

[andreas.singraber]

Hello!

I would like to look at your problem in more detail, can you please provide additional files (OUTCAR, KPOINTS, POTCAR) according to the forum posting guidelines. Thank you!

All the best,
Andreas Singraber