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.
*equil.in
<
http://equil.in> *
equilibrium for density under NTP
&cntrl
imin=0,irest=1,ntx=7,
ntb=2, ntp=1,
pres0=20.0,
taup=0.02,
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,
Liyang
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Received on Sun Feb 05 2017 - 18:00:02 PST
