[gmx-developers] Reaction field questions

[Noel Carrascal]

hi again,
I am interested in the development of improved methods for long range electrostaticinteractions, and I started to look into the code for that.
When I looked into the file name corresponding to reaction field calculations 
/src/gromacs/mdlib/rf_utils.c
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 134:
             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 fshift[CENTRAL]?I can't understand the need of modifying forces by these two terms, does the manualsays anything about this? if so, I missed it. please help.
Thanks
Noel Carrascal,  		 	   		  
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