I have done one NVT molecular simulation for liquid phase propanol and one vacuum simulation for gas phase propanol simulation. However, my calculated heat of vaporization did not match with the experimental value. My liquid phase enthalpy was 21.52 KJ/mol and gas phase enthalpy was 31.6 KJ/mol. So, I got the heat for vaporization is 12.5 KJ/mol whereas, the experimental value is 42.5 KJ/mol. I suspect that the potential energy for liquid phase has having some problem. But, I could not figure that out. My liquid phase potential energy is -13.16 KJ/mol and kinetic energy is 34.68 KJ/mol.
First of all, you need an interaction potential that accounts for hydrogen bonding. There are simple Lennard-Jones- or Mie-type effective potentials that can be used, but these are usually optimized for the liquid phase, and therefore are not very good for the vapour phase. Which potential/force field did you use?
Second, you have to ensure that both phases have the same pressure. You need
NpT simulations for this, and then you have to set the pressure to the equilibrium vapour pressure.
If you do not know the vapour pressure for your propanol model, you can either use a simulation technique that involves fluctuations of the particle number (e.g., grand canonical Monte Carlo or Gibbbs ensemble Monte Carlo) or to obtain the chemical potentials (e.g., Widom's insertion method or thermodynamic integration) and vary the pressure until the chemical potentials of the liquid and the vapour become equal.
S. Lago which paper are you suggesting? can you give the DOI number?
Roberto E. Rozas
I have calculated P*DVvap(T,P) which is a very small value compared with the total value. I my case P*DVvap(T,P) = RT = 2.478 kj/mol
I have no chance to explore much more from my present place.
I suggest that you can also try
Polarizable empirical force field for the primary and secondary alcohol series based on the classical drude model
Anisimov, VM; Vorobyov, IV; (...); MacKerell, AD
Nov-dec 2007 | JOURNAL OF CHEMICAL THEORY AND COMPUTATION 3 (6) , pp.1927-1946
They consider specifically the case you mention, the heats of vaporization of 1-propanol and 1-butanol.
Good luck!
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Condensed Matter Physics
- Soft Matter
- Liquids