Graphene Calculation problem

Message

PhyChemKang · #1 Post by **PhyChemKang** » Fri Oct 01, 2010 4:39 pm

Dear forum members

Currently, i tried to calculate graphene sheet, which has 40 carbon and 18 hydrogen atoms. In these calculation, the size of unit vector is 1 and that of lattice vector is 10 0 0
0 10 0
0 0 10
In the case of this parameter, the optimized structure seems like broken strcutrure, thus, i changed the the sized of unit vertor and lattice vecotor, which are 2 and 7
But the calculation did'nt start due to the follwing message

running on 1 nodes
distr: one band on 1 nodes, 1 groups
vasp.5.2.2 15Apr09 complex
POSCAR found : 2 types and 58 ions
LDA part: xc-table for Pade appr. of Perdew
generate k-points for: 1 1 1
found WAVECAR, reading the header
WAVECAR: different cutoff or change in lattice found
POSCAR, INCAR and KPOINTS ok, starting setup
WARNING: small aliasing (wrap around) errors must be expected
FFT: planning ...( 1 )
reading WAVECAR
the WAVECAR file was read sucessfully
initial charge from wavefunction
entering main loop
N E dE d eps ncg rms rms(c)
/opt/mpich/intel/bin/mpirun.ch_p4: line 243: 24008 Segmentation fault "/home/jin/moon/Graphene/vasp" -p4pg "/home/jin/moon/Graphene/PI23946" -p4wd "/home/jin/moon/Graphene"

how do i have to do for calculation

metosa · #2 Post by **metosa** » Sat Oct 02, 2010 8:30 am

Graphene has hexagonal lattice so

10 0 0
0 10 0
0 0 10

is NONSE for graphene.

You should start with a reasonable lattice and atomic positions....

PhyChemKang · #3 Post by **PhyChemKang** » Sat Oct 02, 2010 12:16 pm

metosa// I confirmed the atomic position. There is no problem. I also tried to change the lattice vector morethan 10. But I always saw same message
/opt/mpich/intel/bin/mpirun.ch_p4: line 243: 24008 Segmentation fault "/home/jin/moon/Graphene/vasp" -p4pg "/home/jin/moon/Graphene/PI23946" -p4wd "/home/jin/moon/Graphene"

metosa · #4 Post by **metosa** » Sat Oct 02, 2010 5:27 pm

%-6

NO! NO! NO!

If your structure is periodic, you CANNOT fit 40 C and 18 H atoms in a 10 10 10 cell.

Maximum number of C atoms which can be inserted periodically is 32 as in this image http://unam.bilkent.edu.tr/mt2/random/r ... ONTCAR.png

My relaxed cell parameters for rectangular graphene sheet are like these:

9.8440999999999992 0.0000000000000000 0.0000000000000000
0.0000000000000000 8.5259999999999998 0.0000000000000000
0.0000000000000000 0.0000000000000000 10.0000000000000000

Note that the x and y vectors are NOT equal as in yours !! Examine my CONTCAR here:
http://unam.bilkent.edu.tr/mt2/random/r ... x4/CONTCAR

If you are trying to simulate a graphene flake (which is NOT periodic) you should allow 10 Angst. vacuum spacings in x and y directions....

PhyChemKang · #5 Post by **PhyChemKang** » Sun Oct 03, 2010 6:31 am

metosa// Thanks for your help. Actually, I'm a begginer of VASP program, thus, i don't have enough knowledges for this program. Anyway, your comment is very helpful for me. Thank you^^

metosa · #6 Post by **metosa** » Sun Oct 03, 2010 4:16 pm

OK,

I suggest you to always visualize your structure by using programs such as p4vasp or VESTA. If you cannot visualize your POSCAR, it means that your structure is problematic. In addition, you should be very careful with numbers. Always use 0.3333333 instead of 0.33 if the former one is the right one....