[gmx-developers] Reaction field questions
hess at kth.se
Wed Mar 4 10:29:32 CET 2015
On 03/04/2015 09:29 AM, David van der Spoel wrote:
> On 2015-03-04 00:12, Noel Carrascal wrote:
>> hi again,
>> I am interested in the development of improved methods for long range
>> interactions, and I started to look into the code for that.
>> When I looked into the file name corresponding to reaction field
>> It all seems correct and makes absolute sense except for two lines in
>> the code
>> that are inside the function "real RF_excl_correction," lines 133 and
>> 129> ener += qqA*(ek*norm2(dx) - ec);
>> 130> svmul(-2*qqA*ek, dx, df);
>> 131> rvec_inc(f[i], df);
>> 132> rvec_dec(f[k], df);
>> 133> rvec_inc(fshift[ki], df);
>> 134> rvec_dec(fshift[CENTRAL], df);
>> What is the physical significance of modifying df by fshift[ki] and
>> I can't understand the need of modifying forces by these two terms, does
>> the manual
>> says anything about this? if so, I missed it. please help.
>> Noel Carrascal,
> These forces are used to compute the virial and hence the pressure.
> Having said that, if you are interested in improved methods for long
> range forces, why are you looking at reaction fields?
Note that you misinterpreted the rvec operations: fshift is being
modified, not df. The pdf manual has a section on shift force calculation.
Furthermore, this code is only used with the group cut-off scheme, which
has been superseded by the Verlet cut-off scheme. Exclusion corrections
now happen inside the nbnxn non-bonded kernels.
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