Enthalpy of vaporization calculation in CP2K

[bharat]

Thank you Janos for your helpful suggestions. I am using PM3 as a reference 
calculation. It's not giving experimental enthalpy of vaporization.

Bharat


On Monday, December 8, 2014 12:58:54 PM UTC-5, Jano... at googlemail.com 
wrote:
>
> Dear Bharat,
>
> I am not convinced about the usage of semiempericals like PM3 for such a 
> purpose, but it is your business... 
> Concerning the approach:
> Calculating internal energy is simply calculating the average of the total 
> energy.  But, as the average of the kinetic energy is defined on a given 
> temperature (I assume, you run NVT simulations), I usually calculate the 
> average of the potential energy. The contribution from kinetic energy 
> should cancel when you subtract the liquid phase value from the gas phase 
> value.
>
> Both potential energy and total energy are reported in the *.ener file in 
> cp2k.
>
> Otherwise do you get the right value by simply adding RT to dU? Just to 
> test your approximation:
> why don't you add d(pV), that you can calculate from experimental 
> densities.
>
>
> Janos
>
> On Monday, December 8, 2014 3:43:56 PM UTC+1, bharat wrote:
>>
>> Hi Samuel,
>> It's a semiempirical calculation. I does not have any functional forms 
>> like GGA or hybrid. Calculation is correct because I was able to reproduce 
>> other properties. Isn't internal energy "Total energy" in CP2K? if not how 
>> do I calculate internal energy from cp2k results?
>>
>> Thanks.
>>
>> Bharat
>>
>> On Monday, December 8, 2014 3:52:56 AM UTC-5, Samuel Andermatt wrote:
>>>
>>> You will need to post your input and output files. Do you do GGA or 
>>> hybrid calculations, how do you account for the vdW forces?
>>>
>>> On Friday, December 5, 2014 4:17:45 PM UTC+1, bharat wrote:
>>>>
>>>> Hello,
>>>> This is friendly reminder. Any suggestions?
>>>>
>>>> Bharat
>>>>
>>>> On Wednesday, December 3, 2014 12:56:10 PM UTC-5, bharat wrote:
>>>>>
>>>>> 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 missing?
>>>>>
>>>>> Thank you.
>>>>>
>>>>> Bharat 
>>>>>
>>>>>
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