I'm new to DFT calculations and trying to produce the Equation of State curves (e.g. Pressure vs Volume) of Graphite. I started relaxing the system with ISIF=3 and then gradually scaled up and down the relaxed cell (with ISIF=4) in order to create the different points on the PV curve. However, my PV curve demonstrates abnormal spikes and I couldn't find out the issue. I was able to produce the PV curve for Diamond and it came out smoothly following the same procedure. Any advice is highly appreciated. I'm using PAW_PEB for carbon.
My INCAR for initial relaxation looks like this,
SYSTEM= C_graphite PREC= A ENCUT= 400.0 EDIFF= 1e-6 IBRION= 2 ISIF= 3 NSW= 100 ISMEAR= 0 ; SIGMA = 0.05 ISTART=0 POTIM= 0.5 LCHARG= .FALSE. LWAVE= .FALSE. LREAL= .FALSE. EDIFFG = -1e-2 ISYM=0
And POSCAR looks like this for Graphite,
C4 1.0 1.2336456308015413 -2.1367369110836267 0.0000000000000000 1.2336456308015413 2.1367369110836267 0.0000000000000000 0.0000000000000000 0.0000000000000000 7.8030730000000004 C 4 direct 0.0000000000000000 0.0000000000000000 0.2500000000000000 C 0.0000000000000000 0.0000000000000000 0.7500000000000000 C 0.3333333333333333 0.6666666666666666 0.2500000000000000 C 0.6666666666666667 0.3333333333333334 0.7500000000000000 C
I have used automatic k-point mesh as follows,
EA 0 Auto 32
Can you guys please advise me to find out my mistake?
Thank you very much.