[gmx-users] mutiple dihedral terms

[Mark Abraham]

On 20/11/2010 6:40 AM, Justin A. Lemkul wrote:
>
>
> Sanku M wrote:
>> Hi,
>>   I have a molecule consisting of 4 atoms  1-2-3-4 .
>> The paper parameterizing the molecule has reported combination of 
>> following multiple set of dihedral terms by fitting the dihedral 
>> angle distributions of this tetra-atomic molecule :
>>       theta0         K     n
>>     180           1.96   1      0              0.18   2
>>      0             0.33    3
>>      0            0.12     4
>>
>> Now, I was trying to incorporate this dihedral terms in my gromacs 
>> topology file: My question is , is it possible to use Proper dihedral 
>> angles  four time for the same dihdral angles :
>> i.e
>> If I write the dihedral part of  topology file in the following way, 
>> will it be OK so that Gromacs will add them up ?
>> [dihedrals]
>> 1  2  3  4     1    180.00    1.96   1
>> 1  2  3  4     1     0    0.18   2
>> 1  2  3  4     1     0    0.33   3
>> 1  2  3  4     1     0    0.12   4
>>
>> Or, will it consider only the last one ? 
>
> They are additive.  Surely this is in the manual somewhere.

Indeed. Sanku can also try several 1-step runs that add in more of them, 
and see that the energy is changing.

Mark

>
> -Justin
>
>> If it is not the case, Am I supposed to convert them into Ryckert 
>> Bellman type and sum them up ?
>> Any suggestion will be helpful.
>> Sanku
>>
>