[AMBER] EPM2 Force field for CO2

From: Liyang Zhu <liyangzhu.lbl.gov>
Date: Sun, 5 Feb 2017 17:34:59 -0800

Dear all,

I am testing a pure CO2 system.

The force field of CO2 was generated using antechamber, however, when
equilibrium the system under NTP, the density is much high than
expected.The density should be 0.8 g/ml at 333K and 20 atm. But the
equilibrated density was around 1.0~1.2 for the parameters from both
gaff.dat and gaff2.dat.

<http://equil.in> *
equilibrium for density under NTP
 ntb=2, ntp=1,
 cut=12.0, ntr=0,
 ntc=2, ntf=2,
 tempi=333.0, temp0=333.0,
 ntt=3, gamma_ln=1.0,
 nstlim=500000, dt=0.002, ig=-1,
 ntpr=100, ntwx=500, ntwr=1000
*/ *

Typically the VDW parameters in Amber is as follows:

* angstrom kcal/mol *
c1 1.9525 0.1596
*o 1.7101 0.1463*

And get to know that there is a EPM2 model for CO2 used in many papers,
which is high accurate for density properties. However, the parameters can
not be used in amber correctly, because there is always a error of sander
bomb during NTP equilibrium. The parameter of EPM2 is as follows:

* angstrom kcal/mol *
c1 2.757 0.0558
*o 3.033 0.1600*

This parameter is largely different from the amber parameter, but the VDW
equation used in literature is the same as amber. I also multiply VDW radii
to 2^(-1/6), still not work (sander bomb😅).

Does anyone tell me why I can not use this EPM2 parameter in amber?

Thanks a lot,
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Received on Sun Feb 05 2017 - 18:00:02 PST
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