From: Faramarz Joodaki (fjoodaki_at_my.uri.edu)
Date: Fri Jul 07 2017 - 18:04:48 CDT
Hi everyone!
I have a question about the cross-term in NAMD source code. From the source
code, file "ComputeCrossterms.C", I found that NAMD is using bicubic spline
interpolation to find the energy and first derivative of cross-term energy
respect to Phi and Psi.
As I found:
dU/d(phi) is
fx += dxa[i] * ya[j] * table[ij].d00
+ dxb[i] * ya[j] * table[ij].d10
+ dxa[i] * yb[j] * table[ij].d01
+ dxb[i] * yb[j] * table[ij].d11;
and dU/d(psi) is
fy += xa[i] * dya[j] * table[ij].d00
+ xb[i] * dya[j] * table[ij].d10
+ xa[i] * dyb[j] * table[ij].d01
+ xb[i] * dyb[j] * table[ij].d11;
I would like to calculate the second derivative respect to Phi and Psi.
According to these formulae, for example, I am using to use below formula
for d2U/d(Psi)2
fyy += xa[i] * d2ya[j] * table[ij].d00
+ xb[i] * d2ya[j] * table[ij].d10
+ xa[i] * d2yb[j] * table[ij].d01
+ xb[i] * d2yb[j] * table[ij].d11;
I would be so grateful if you could guide is the way of my thought is
correct?
Best Regards,
Faramarz
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