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[lammps-users] ion pair simulation
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[lammps-users] ion pair simulation

From: Hossein Geraili <geraili.hsn@...24...>
Date: Sun, 8 Oct 2017 14:48:38 +0330

Dear all,
I am calculating Internal energy using a derivation of an equation of state, and I need to calculate a temperature dependent parameter( which is total energy in the ideal gas state(F(T)):
Ein=∫Pin/rho^2 d rho +F(T)= RT{ (e*rho^2)+(f*rho)+(g*rho^4)}+F(T)
That F(T) is the ideal contribution of internal energy since it is equal to total energy at zero density
Also, the resulted Cp from the derivation of this Ein is:

Cp=R{ (a*rho^2)+(b*rho)+(c*rho^4)}+F'(T)
This Cp has F'(T) which is temperature derivation of F(T).
. I simulated bulk for the non-ideal part with 300 molecules of [BMIM][PF6], and it is totally ok. But for the ideal part(F(T) or F'(T)) at gas state, energies are not consistent and so meaningful, because as I calculate F(T) from experimental data, I found out that total energy should be negative, which is now positive in Lammps(for one ion pair), and smaller than what it is now. I used a single pair of the ion at the nonperiodic boundary condition, but the energies( bond, angle, dihedral, ...) are not the same as bulk which I think they should be since they are intramolecular quantities(they are slightly bigger than what they should be as regard to article that I use)(also non-bonded intramolecular energies like VdW and electrostatic are slightly different). Also keeping the temperature constant is so difficult, but it is not a problem, and I can derive any F(T) or F'(T) with fitting them into a polynomial. I already used 4RT for the Cp as F'(T)(or ideal contribution of Cp), but it did not work, so I want to use Lammps to calculate energies at each temperature and use their energy as F(T), and finally, I would use the derivation of F(T) instead of F'(T)for the ideal contribution of Cp.
any suggestion or comment would be appreciated.
best regards

Hosein Geraili Daronkola
M.Sc.Graduated of physical chemistry
Physical Chemistry,
Department of Chemistry,
Sharif University of Technology.

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