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Re^5: Binding Energies for Receptor Ligand Systems

Solntsev Pasha
solntsev@univ.kiev.ua

On Wed Dec 17 '08 5:13pm, Thomas Patko wrote
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>Can you post some sample input and output files for the hessian job runs that will do this and any methodology if possible?

yes sure.
I had made geometry optimization of 1,3,5-tetrazine and then used obtained geometry to make hessian computation. (geometry optimization and hessian computation have been performed at the same level of theory MP2/6-311++G(d,p)). Also it is possible to put hssend=.t. into the $statpt keywords to do computation hessian after geometry optimization.

$CONTRL SCFTYP=RHF RUNTYP=hessian MPLEVL=2 MAXIT=100 MULT=1 $END
$SYSTEM TIMLIM=525600 MEMORY=30000000 $END
$BASIS GBASIS=N311 NGAUSS=6 NDFUNC=1 NPFUNC=1
 DIFFSP=.T. DIFFS=.T. $END
$SCF DIRSCF=.TRUE. FDIFF=.T. SOSCF=.F. $END
$MP2 NCORE=12 $END
$GUESS GUESS=HUCKEL  $END
$DATA
hessian computation mp2/6-311++G(d,p)
DNH 3

C           6.0   0.6480544390   1.1224640926   0.0000000000
N           7.0  -0.6889473520   1.1932926956   0.0000000000
H           1.0   1.1781855477   2.0406791473   0.0000000000
$END

check end of output file and find something like this:

THE HARMONIC ZERO POINT ENERGY IS (SCALED BY   1.000)
       0.070490 HARTREE/MOLECULE    15470.872410 CM**-1/MOLECULE
      44.233488 KCAL/MOL              185.072915 KJ/MOL

> What scaling factor did you use for these MP2 job runs with the large basis sets on the vibrational frequencies to calculate the ZPVE from?

I didn't use ZPVE because it was shown to have to small contribution into formation binding energy, but for more precision data it is useful to include it. I take google and found many useful articles. Some times authors made computation ZPVE at 6-311G(d,p) level of theory, while binding energy and geometry optimization were made at very hight level of theory, like MP2/6-311++G(2d,p) or higher. You should consult with guru in quantum chemistry about this moment and reviewed available literature data.

I am not sure, but i think it is possible to compute binding energy using Gibs's energy (G) instead of total energy.

>I found an example (using a much lower level of theory) that I thought might be germane posted at:

There are many excellent examples available over internet (try google).


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