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<DIV><FONT size=2 face=Tahoma>Hi, all,<BR> I was wondering to
modify Shift electrostatic summation to a new one. The origin Shift form in
Gromacs is like 1/r-1/Rc (Rc is cut-off), I need to modify to
erfc(alpha*r)/r-erfc(alpha*Rc)/Rc, and the original long-range correction of
Shift in code shift_util.c is q^2/(2*Rc) ( something like that ), I need to
q^2*(erfc(alpha*Rc)/(2*Rc)+alpha/sqrt(pi)). So question is:<BR>How the force to
Shift was calculated? Gromacs use the differentiation to energy, got the force
formula, then calculated the force? Or just use the numerical differentiation to
the energy and got it? If is the latter one, I do not need to modify the force
calculation.<BR>And also, the alpha for Ewald summation, is there an option or
parameters to adjust this value?<BR>Hi, Mark and Berk, if I want do modify shift
electrostatic summation as I want, what other files or place do I need to
modify, except shift_util.c and force.c?<BR>Shuangxing Dai</FONT></DIV>
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