VDW_RADIUS in INCAR file

Message

lukasz.rzeznik · #1 Post by **lukasz.rzeznik** » Wed Jan 22, 2014 5:18 pm

Does VDW_RADIUS work in all the cases of Van der Waals corrections or only in the case of Tkatchenko Scheffler vdW correction?

I am trying to calculate the rotational barrier for ethane and in the same time go from ethane to ethene (by increasing one C-H bond length for each C atoms) and I cannot reach the energy barrier which I calculate for simple ethene. So I suspect that the influence of the H atoms from enlarged bonds is to strong especially if the C-H distance is much larger (e.g. 4.8 A) compared to the "normal" distance (1.1 A).

#2 Post by **admin** » Tue Feb 04, 2014 6:48 pm

the van der Waals radius works for Grimme's method as well (DFT-D2)

lukasz.rzeznik · #3 Post by **lukasz.rzeznik** » Mon Feb 17, 2014 5:55 pm

Yes, now I see in the manual. I was concentrated on the vdW-DF, "opt" and vdW-DF2 functionals, as I thought as newer they must be better, but it seems that they do not support VDW_RADIUS option.
<span class='smallblacktext'>[ Edited Mon Feb 17 2014, 05:55PM ]</span>

lukasz.rzeznik · #4 Post by **lukasz.rzeznik** » Wed Feb 19, 2014 7:03 pm

Well, Grimme method (with vdw radius set to 2.3A) produces similar results as optB86b (without vdw radius set).

Is that INCAR files correct? I used them to calculate energy of C2H6 / C2H4 molecules of a certain geometry (set independently by my in another program).

For optB86b:

general:
System = Ethane
ISTART = 0

IBRION = 2
NSW = 1 #I just need an energy of a certain
molecule configuration so 1 calculation
EDIFFG = 1.0e-05
EDIFF = 1.0E-05

GGA = MK
PARAM1 = 0.1234
PARAM2 = 1.0000
PREC = normal
ENCUT = 450
NELMIN = 5
IALGO = 38
ISMEAR = 0; SIGMA = 0.1
LREAL = .FALSE.
ADDGRID = .TRUE.
LWAVE = .FALSE.
LCHARG = .FALSE.
LUSE_VDW= .TRUE.
AGGAC = 0.0000

For Grimme:

general:
System = Ethane
ISTART = 0

IBRION = 2
NSW = 1
EDIFFG = 1.0e-05
EDIFF = 1.0E-05

GGA = 91
PREC = normal
ENCUT = 450
NELMIN = 5
IALGO = 38
ISMEAR = 0; SIGMA = 0.1
LREAL = .FALSE.
ADDGRID = .TRUE.
LWAVE = .FALSE.
LCHARG = .FALSE.
LVDW = .TRUE.
VDW_RADIUS = 2.3

KPOINTS:

K-Points
0
1 1 1
0 0 0

Same POTCAR (PAW_GGA C 05Jan2001 and PAW_GGA for C), but for optB86b uses vdw_kernel.bindat.

lukasz.rzeznik · #5 Post by **lukasz.rzeznik** » Fri Jun 13, 2014 5:06 pm

Calculating the rotational barrier for ethene using optB86b.

I realized that the INCAR above concerns the self-consistent calculations (ionic relaxation). When I create WAVECAR and CHRGCAR (ISPIN=1, ICHARG=2) and then run non self-consistent calculations (electronic relaxation) (ISPIN=2, ICHARG=1) I can improve the rotational barrier for ethene (~71 kcal/mol). However I see some differencies in mag values. It is mag=2 for angles close to 90 deg and mag=0 for other angles (0-60, >130). I am not sure if it is related with pi bond breaking during rotation of the molecule.

Does it make sens to try to improve the calculations more by applying the spin-orbit coupling?

---------------------------------------

INCAR (for self-consistent run):

ISTART = 0 # start job from scratch # WAVECAR file

ICHARG = 2
ISPIN = 1

IBRION = 2 # CG optimisation algorithm
NSW = 0 # Number of ionic steps
EDIFFG = 1.0e-06 # Force threshold (A/eV)
EDIFF = 1.0E-06 # E threshold for electron (eV)

GGA = MK # GGA Perdew-Burke-Ernuerhof funnctional
PARAM1 = 0.1234
PARAM2 = 1.0000
PREC = normal # Precision accurate for phonon calcs
ENCUT = 450 # Planewave energy cutoff
NELMIN = 5
IALGO = 38
ISMEAR = 0; SIGMA = 0.1 # method to determine partial occupancies
LREAL = .FALSE. # Real space projection
ADDGRID = .TRUE.
LWAVE = .TRUE.
LCHARG = .TRUE.
LUSE_VDW= .TRUE.
AGGAC = 0.0000

-----------------------------

INCAR (for non self-consistent run):

ISTART = 2 # start job from scratch # WAVECAR file

ICHARG = 1
ISPIN = 2

IBRION = 2 # CG optimisation algorithm
NSW = 0 # Number of ionic steps
EDIFFG = 1.0e-06 # Force threshold (A/eV)
EDIFF = 1.0E-06 # E threshold for electron (eV)

GGA = MK # GGA Perdew-Burke-Ernuerhof funnctional
PARAM1 = 0.1234
PARAM2 = 1.0000
PREC = normal # Precision accurate for phonon calcs
ENCUT = 450 # Planewave energy cutoff
NELMIN = 5
IALGO = 38
ISMEAR = 0; SIGMA = 0.1 # method to determine partial occupancies
LREAL = .FALSE. # Real space projection
ADDGRID = .TRUE.
LWAVE = .FALSE.
LCHARG = .FALSE.
LUSE_VDW= .TRUE.
AGGAC = 0.0000

lukasz.rzeznik · #6 Post by **lukasz.rzeznik** » Mon Jun 16, 2014 4:03 pm

I also see the comment:
"No down-spin wavefunctions found --> setting down-spin equal up-spin ...
charge-density read from file: ethene
magnetization density of overlapping atoms calculated "
in the main output file (JOBNAME.oJOB-ID)