Just to clarify that 49.51 kcal/(mol*Rad^2) is based on the Seminario method.
While based on the Z-matrix method the value is 55.84 kcal/(mol*Rad^2).
All of these values are based on the Hessian matrix obtained from an
optimized single water molecule structure based on the B3LYP/6-31G* level
of theory with Integral=(Grid=UltraFine) in G09.
> On Apr 5, 2018, at 8:29 AM, pengfei li <ldsoar1990.gmail.com> wrote:
>
> Right, I think I missed a point that whether SHAKE is used or not, TIP3P model is set as rigid
> (since H-H bond exists there). So the HW-OW-HW force constant is just a placeholder for it.
>
> HW-OW-HW has angle force constant as 37.95 kcal/(mol*Rad^2) in the SPC/Fw model,
> which is close to the B3LYP/6-31G* level of theory calculated Hessian matrix predicted
> force constant (which is 49.51 kcal/(mol*Rad^2)).
>
>> On Apr 5, 2018, at 8:25 AM, David Cerutti <dscerutti.gmail.com> wrote:
>>
>> Look up the SPC-Fw paper by Yujie Wu. The angle constant, which is
>> probably tuned to get bulk properties just like everything else, would be
>> interdependent on the charges and vdW parameters. If you want to fit an
>> angle parameter to reproduce specific quantum data, use mdgx and see what
>> comes out. Another thing to point out for avid readers is that TIP3P and
>> other rigid models have a bond between the hydrogens to enforce their
>> geometry.
>>
>> On Wed, Apr 4, 2018 at 8:22 PM, pengfei li <ldsoar1990.gmail.com> wrote:
>>
>>> Hi Carlos and Dave,
>>>
>>> That is a good point. It seems it doesn’t matter when using SHAKE since it
>>> is rigid.
>>> I am just curious if SHAKE was not used, is 50.0 kcal/(mol*Rad^2) a better
>>> choice
>>> than 100.0 kcal/(mol*Rad^2)?
>>>
>>> Best regards,
>>> Pengfei
>>>
>>>> On Apr 5, 2018, at 8:20 AM, David Cerutti <dscerutti.gmail.com> wrote:
>>>>
>>>> I'm in agreement with Carlos--the force constants for rigid water models
>>>> are placeholders. For SPC-Fw, the angle constant does matter, but
>>>> understand it's essentially making a fixed charge water model
>>> polarizable,
>>>> in a sense.
>>>>
>>>> On Wed, Apr 4, 2018 at 8:17 PM, Carlos Simmerling <
>>>> carlos.simmerling.gmail.com> wrote:
>>>>
>>>>> Since the water is rigid and there is a bond between the H atoms, does
>>> the
>>>>> force constant matter?
>>>>>
>>>>> On Wed, Apr 4, 2018, 8:14 PM pengfei li <ldsoar1990.gmail.com> wrote:
>>>>>
>>>>>> Hi Everyone,
>>>>>>
>>>>>> Does anybody know how does the force constant for HW-OW-HW angle come
>>>>>> from? I found it is 100.0 kcal/(mol*Rad^2) but 50.0 kcal/(mol*Rad^2)
>>> is a
>>>>>> more reasonable choice based on Hessian matrix of B3LYP/6-31G* level of
>>>>>> calculations. However, I could not find a value in the original
>>>>> TIP3P/TIP4P
>>>>>> article (Jorgensen, W. L.; Chandrasekhar, J.; Madura, J. D.; Impey, R.
>>>>> W.;
>>>>>> Klein, M. L. J. Chem. Phys. 1983, 79, 926-935.). So I am just curious
>>>>> about
>>>>>> what does the original value come from? Thanks!
>>>>>>
>>>>>> Best regards,
>>>>>> Pengfei
>>>>>> _______________________________________________
>>>>>> AMBER-Developers mailing list
>>>>>> AMBER-Developers.ambermd.org
>>>>>> http://lists.ambermd.org/mailman/listinfo/amber-developers
>>>>>>
>>>>> _______________________________________________
>>>>> AMBER-Developers mailing list
>>>>> AMBER-Developers.ambermd.org
>>>>> http://lists.ambermd.org/mailman/listinfo/amber-developers
>>>>>
>>>> _______________________________________________
>>>> AMBER-Developers mailing list
>>>> AMBER-Developers.ambermd.org
>>>> http://lists.ambermd.org/mailman/listinfo/amber-developers
>>>
>>>
>>> _______________________________________________
>>> AMBER-Developers mailing list
>>> AMBER-Developers.ambermd.org
>>> http://lists.ambermd.org/mailman/listinfo/amber-developers
>>>
>> _______________________________________________
>> AMBER-Developers mailing list
>> AMBER-Developers.ambermd.org
>> http://lists.ambermd.org/mailman/listinfo/amber-developers
>
_______________________________________________
AMBER-Developers mailing list
AMBER-Developers.ambermd.org
http://lists.ambermd.org/mailman/listinfo/amber-developers
Received on Wed Apr 04 2018 - 18:30:06 PDT
