[gmx-users] Enthalpy of Vaporization

Justin Lemkul jalemkul at vt.edu
Tue Oct 6 16:47:04 CEST 2015

On 10/5/15 11:30 PM, Pallavi Banerjee wrote:
> My system is one molecule of Propanamide. I need to see if my force field
> makes the molecule water soluble or not, for which I would need its
> cohesive energy, and this in turn would require the heat of vaporization.
> So, I should include the total potential energy for both gas and liquid
> phase in the following calculation : (U gas - U liq) / Nmol + RT. Is that
> right?

No.  Mind your parenthesis.  The liquid phase has Nmol molecules, hence you 
divide the total potential of the liquid phase Uliq by Nmol.  You only have one 
molecule in the gas phase.  Perhaps more pedantically:

DHvap = <U gas> - ( <U liq> / Nmol ) + RT

Angle brackets denote the time average.



Justin A. Lemkul, Ph.D.
Ruth L. Kirschstein NRSA Postdoctoral Fellow

Department of Pharmaceutical Sciences
School of Pharmacy
Health Sciences Facility II, Room 629
University of Maryland, Baltimore
20 Penn St.
Baltimore, MD 21201

jalemkul at outerbanks.umaryland.edu | (410) 706-7441


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