Major Total Energy Differences - Dispersion Correction

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kmkumar · #1 Post by **kmkumar** » Thu Mar 31, 2011 10:56 am

Dear Collegues,

I started a calculation by setting the tag
LVDW=.TRUE.
and looked into the total energy which differs almost like 16.4 eV from the calculation in which this tag is removed.

I don't think this is reasonable, and i do not know where i am going wrong.

Could you please help.

Here are some additional details.

Total Energy without Dispersion Correction = -1946.740941 eV
Total Energy With Dispersion Correction = -1962.968314 eV

From OUTCAR

Grimme's potential added to compensate for missing vdW interactions
-------------------------------------------------------------------

Parameters for Grimme's potential:
C6(Jnm^6/mol) R0(A)
-----------------------------
O 0.700 1.342
Si 9.230 1.716
C 1.750 1.452
^@^@ 0.000 0.000
H 0.140 1.001

Cutoff radius: 30.000 A
Global scaling factor: 0.750 A
Parameter d: 20.000 A
Number of pair interactions contributing to Grimme's potential: 427374
Estimated vdW energy (eV): -16.36075

I also did calculations by reducing the cutoff radius but that didn't help me too much..

Please help.

alex · #2 Post by **alex** » Thu Mar 31, 2011 4:52 pm

Get the Grimme papers, calculate one pair by hand and judge for yourself. Reason will come.

Cheers,

alex