[gmx-users] gas phase force field

[Justin Lemkul]

On 6/22/15 8:47 AM, V.V.Chaban wrote:
> Not all organics is polar, Justin. :-)
>

Obviously.

> Hydrogen bond length, and hence, energy are well limited by sigma in
> LJ. Even if dipole moments are overestimated by 20%, this should not
> lead to a proportional increase in the hydrogen bond strength.
>

Actually, it can and does.  I used a specific example that we know quite well. 
Overestimation of dipole moments in vicinal alcohols depresses the gas-phase 
energy leading to incorrect dHvap.  This is a trend in additive force fields, 
and we consistently see failures of additive models to respond to different 
conditions as we develop our polarizable force fields (which correctly reproduce 
both gas and liquid phase properties).  Most force fields are geared towards 
condensed phase properties.  Of course not all models reflect the same 
properties, but one needs to carefully evaluate the proper behavior in the gas 
phase based on available data.  Additive models are generally incapable of 
responding to both gas and liquid states.

-Justin

>
>
>
>
> On Sun, Jun 21, 2015 at 9:52 PM, Justin Lemkul <jalemkul at vt.edu> wrote:
>>
>>
>> On 6/21/15 9:07 AM, V.V.Chaban wrote:
>>>
>>> Actually, any existing field, since all of them -- to this or that
>>> extent -- were cteated under cluster-in-vacuum' approach.
>>>
>>
>> While most biomolecular force fields have their origins in gas-phase QM,
>> most ultimately target condensed-phase properties.  Additive force fields
>> thus must overestimate gas-phase dipole moments on the order of ~20% or more
>> to capture proper liquid-phase properties.  This is a reason why one will
>> see overly strong intramolecular hydrogen bonding in polyols, etc.
>>
>> -Justin
>>
>>>
>>>
>>> On Sun, Jun 21, 2015 at 3:02 AM, Swapnil Kate
>>> <swapnilkate at rocketmail.com> wrote:
>>>>
>>>> Hello all,
>>>> Can any one please tell me which force fields are used for accurate
>>>> prediction of gas phases on organics?
>>>> RegardsSwapnil
>>>>
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>>
>> --
>> ==================================================
>>
>> 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
>>
>> ==================================================
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>> Gromacs Users mailing list
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-- 
==================================================

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

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