Enthalpy of vaporization calculation in CP2K

bharat bharats... at gmail.com
Wed Dec 3 17:56:10 UTC 2014

Hello Experts,

I am trying to reproduce Enthalpy of vaporization using PM3.
Here are my calculation: 
(I took Total energy value from CP2K output file as an Internal energy, 
average is calculated over the MD. Experimental density is used for the 
constant volume for both liquid and vapor calculation). Am I taking correct 
energy value for internal energy? 

U_vapor(Avg) = -20797.3 eV 
U_liquid(Avg) = -20802.9 eV

Delta_U = 5.6 eV 
I divided with 64 (# of water molecules) and converted to kcal/mol
= 2.02 kcal/mol

I got the half value (reported value is 4.00 kcal/mol in G. Murdachaew et 
al. J. Phys. Chem. A 115, 6046 (2011)). Because of this value, I got only 
~2.60 kcal/mol (RT= ~0.60 kcal/mol) of enthalpy of vaporization (Delta_H = 
delta_U + RT). 

Can anyone please tell me where I am doing wrong? Where is the factor 2 

Thank you.


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