Right or Wrong?

Message

rezorva · #1 Post by **rezorva** » Mon Jan 30, 2012 8:34 am

Dear vasp?users,

Im trying to do a geometric optimization for BCN supercell, but I would like to know if my parameter are right or wrong... My different INPUT files are:

INCAR file:
$SYSTEM = B C N
NELMIN = 4
EDIFF = 1E-04
EDIFFG = -1E-2
PREC = medium
IBRION = 1
ISIF = 3
NSW = 50
ISMEAR = 0
LCHARG =.FALSE.
LREAL= Auto

KPOINTS:
Automatic generation
0
Monkhorst Pack
1 1 10
0 0 0

POSCAR:
BCNHo1
1.0
15.9790000916 0.0000000000 0.0000000000
0.0000000000 27.9549999237 0.0000000000
0.0000000000 0.0000000000 4.5999999046
B C N
17 122 17
Direct
0.194319993 0.172151998 0.500000000
0.270732999 0.247808993 0.500000000
0.347146004 0.172151998 0.500000000
0.423557997 0.247808993 0.500000000
0.499971002 0.172151998 0.500000000
0.347146004 0.323466003 0.500000000
0.423557997 0.449562013 0.500000000
0.347146004 0.525219023 0.500000000
0.423557997 0.600875974 0.500000000
0.499971002 0.525219023 0.500000000
0.576447010 0.449562013 0.500000000
0.652858973 0.525219023 0.500000000
0.576447010 0.600875974 0.500000000
0.729272008 0.600875974 0.500000000
0.270732999 0.600875974 0.500000000
0.499971002 0.323466003 0.500000000
0.499971002 0.676533997 0.500000000
0.194319993 0.071275003 0.500000000
0.117907003 0.096493997 0.500000000
0.041494001 0.071275003 0.500000000
0.499971002 0.071275003 0.500000000
0.423557997 0.096493997 0.500000000
0.347146004 0.071275003 0.500000000
0.270732999 0.096493997 0.500000000
0.117907003 0.146933004 0.500000000
0.041494001 0.222589999 0.500000000
0.041494001 0.172151998 0.500000000
0.805684984 0.071275003 0.500000000
0.729272008 0.096493997 0.500000000
0.652858973 0.071275003 0.500000000
0.576447010 0.146933004 0.500000000
0.576447010 0.096493997 0.500000000
0.117907003 0.298247010 0.500000000
0.117907003 0.247808993 0.500000000
0.041494999 0.323466003 0.500000000
0.958510995 0.071275003 0.500000000
0.882098019 0.146933004 0.500000000
0.882098019 0.096493997 0.500000000
0.805684984 0.172151998 0.500000000
0.729272008 0.146933004 0.500000000
0.652858973 0.222589999 0.500000000
0.652858973 0.172151998 0.500000000
0.576447010 0.247808993 0.500000000
0.194319993 0.373903990 0.500000000
0.194319993 0.323466003 0.500000000
0.117907003 0.399123996 0.500000000
0.041494999 0.373903990 0.500000000
0.958510995 0.222589999 0.500000000
0.958510995 0.172151998 0.500000000
0.882098019 0.247808993 0.500000000
0.805684984 0.222589999 0.500000000
0.729272008 0.298247010 0.500000000
0.729272008 0.247808993 0.500000000
0.652858973 0.323466003 0.500000000
0.576447010 0.298247010 0.500000000
0.499971002 0.373903990 0.500000000
0.423557997 0.399123996 0.500000000
0.347146004 0.373903990 0.500000000
0.270732999 0.449562013 0.500000000
0.270732999 0.399123996 0.500000000
0.194319993 0.474781007 0.500000000
0.117907003 0.449562013 0.500000000
0.041494999 0.525219023 0.500000000
0.041494999 0.474781007 0.500000000
0.958510995 0.323466003 0.500000000
0.882098019 0.298247010 0.500000000
0.805684984 0.373903990 0.500000000
0.805684984 0.323466003 0.500000000
0.729272008 0.399123996 0.500000000
0.652858973 0.373903990 0.500000000
0.576447010 0.399123996 0.500000000
0.194319993 0.525219023 0.500000000
0.117907003 0.600875974 0.500000000
0.117907003 0.550437987 0.500000000
0.041494999 0.626096010 0.500000000
0.958510995 0.373903990 0.500000000
0.882098019 0.449562013 0.500000000
0.882098019 0.399123996 0.500000000
0.805684984 0.474781007 0.500000000
0.729272008 0.449562013 0.500000000
0.194319993 0.676533997 0.500000000
0.194319993 0.626096010 0.500000000
0.117907003 0.701753020 0.500000000
0.041494999 0.676533997 0.500000000
0.958510995 0.525219023 0.500000000
0.958510995 0.474781007 0.500000000
0.882098019 0.550437987 0.500000000
0.805684984 0.525219023 0.500000000
0.423557997 0.701753020 0.500000000
0.347146004 0.676533997 0.500000000
0.270732999 0.752191007 0.500000000
0.270732999 0.701753020 0.500000000
0.194319993 0.777409971 0.500000000
0.117907003 0.752191007 0.500000000
0.041494999 0.827848017 0.500000000
0.041494999 0.777409971 0.500000000
0.958510995 0.626094997 0.500000000
0.882098019 0.600875974 0.500000000
0.805684984 0.676533997 0.500000000
0.805684984 0.626094997 0.500000000
0.729272008 0.701753020 0.500000000
0.652858973 0.676533997 0.500000000
0.576447010 0.752191007 0.500000000
0.576447010 0.701753020 0.500000000
0.499971002 0.777409971 0.500000000
0.423557997 0.752191007 0.500000000
0.347146004 0.827848017 0.500000000
0.347146004 0.777409971 0.500000000
0.270732999 0.853066981 0.500000000
0.194319993 0.827848017 0.500000000
0.117907003 0.903505981 0.500000000
0.117907003 0.853066981 0.500000000
0.041494999 0.928725004 0.500000000
0.958510995 0.676533997 0.500000000
0.882098019 0.752191007 0.500000000
0.882098019 0.701753020 0.500000000
0.805684984 0.777409971 0.500000000
0.729272008 0.752191007 0.500000000
0.652858973 0.827848017 0.500000000
0.652858973 0.777409971 0.500000000
0.576447010 0.853066981 0.500000000
0.499971002 0.827848017 0.500000000
0.423559010 0.903505981 0.500000000
0.423559010 0.853066981 0.500000000
0.347146004 0.928725004 0.500000000
0.270732999 0.903505981 0.500000000
0.194319993 0.928725004 0.500000000
0.958510995 0.827848017 0.500000000
0.958510995 0.777409971 0.500000000
0.882098019 0.853066981 0.500000000
0.805684984 0.827848017 0.500000000
0.729272008 0.903505981 0.500000000
0.729272008 0.853066981 0.500000000
0.652858973 0.928725004 0.500000000
0.576447010 0.903505981 0.500000000
0.499971002 0.928725004 0.500000000
0.958510995 0.928725004 0.500000000
0.882098019 0.903505981 0.500000000
0.805684984 0.928725004 0.500000000
0.194319993 0.222589999 0.500000000
0.347146004 0.222589999 0.500000000
0.270732999 0.146933004 0.500000000
0.270732999 0.298247010 0.500000000
0.423557997 0.298247010 0.500000000
0.499971002 0.222589999 0.500000000
0.423557997 0.146933004 0.500000000
0.423557997 0.550437987 0.500000000
0.576447010 0.550437987 0.500000000
0.499971002 0.626096010 0.500000000
0.499971002 0.474781007 0.500000000
0.652858973 0.474781007 0.500000000
0.347146004 0.474781007 0.500000000
0.270732999 0.550437987 0.500000000
0.347146004 0.626096010 0.500000000
0.652858973 0.626096010 0.500000000
0.729272008 0.550437987 0.500000000

Please help me... Thank you so much in advance...

#2 Post by **admin** » Mon Jan 30, 2012 12:10 pm

Hve you displayed your structure? In the x-direction the structure is continuous wit four-membered rings between the cells. In the y-direction the structure is discontinuous with the gap of 4A between the cells. Is this what you want to calculate?
Realaxation of a large cell runs well with just single k-point.
[ Edited Mon Jan 30 2012, 12:15PM ]

rezorva · #3 Post by **rezorva** » Mon Jan 30, 2012 1:17 pm

Hi admin,

Thank you for your answer... I would like to calculate or to do a geometric optimization using a graphene layer...

vistawanted · #4 Post by **vistawanted** » Tue Jan 31, 2012 5:10 pm

At least, in my point of view, the c-axes is too small for "single-layer" simulation (of cource, if you want to work on several layers structure, you'd better using graphite symmetry, P63mc space group). Normally, the "vacumm slab" for graphene layer calculations is 10~20 Angstrom.
Furthermore, since graphene-like structure is hexagonal, why not set a0 and a1 vectors as: a0*(1.0, 0.0, 0.0) and a1*(-0.5, sqrt(3)/2, 0.0) ?
I am not sure whether there are something special in VASP, but based on common ab-initio knowledge, using hex-coordinate based model is better in graphene layer field to achieve the better 3D periodicity expansion.