[gmx-users] Enthalpy of Vaporization

[Justin Lemkul]

On 10/5/15 2:01 PM, Rasoul Nasiri wrote:
> On Mon, Oct 5, 2015 at 6:52 PM, Justin Lemkul <jalemkul at vt.edu> wrote:
>
>>
>>
>> On 10/5/15 1:50 PM, Pallavi Banerjee wrote:
>>
>>> Correct me if I am wrong, please. Ugas would be obtained from a simulation
>>> of a single molecule in vacuum. And U liq would be the total potential
>>> energy of the system (which is given by g_energy) minus the total bonded
>>> potential energy (bonds+angles+dihedrals). Am I thinking right?
>>>
>>>
>> No.  It's the actual potential energy.  You need the whole potential
>> energy to account for flexibility in the molecule.
>>
>>
> Hopefully FFs can do this because of the anharmonicity effects caused by
> multi-structural effects (e.g., many coupling of torsions). This
> scenario will be serious when T goes up.
>

Indeed it depends to some extent on the size, flexibility, and chemical 
composition of the molecule.  Additive FFs will inherently overestimate dipole 
moments to account for a lack of polarization response, so generally very polar 
molecules have poor DHvap values with additive models.  Simple hydrophobics are 
easier and often agree better with experimental data.

-Justin

-- 
==================================================

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
http://mackerell.umaryland.edu/~jalemkul

==================================================