[gmx-users] dihedrals: from OPLS to Ryckaert-Belleman

Markus O Kaukonen mokaukon at cc.helsinki.fi
Tue Nov 2 11:15:01 CET 2004


Dear All,

There are instructions in the Gromacs User Manuallpages 62-63
how to convert from OPLS to Ryckaert-Belleman dihedrals.

However, I did not get how to convert the opls phase (gamma)
which is usually 0 or 180 degrees to 'something' in Ryckaert-Belleman.
(Opls for of the potential:
weiner-JACS-v106-pp-765-784-y1984 EQ 1
mu-JPhysChemB-v107-pp5064-5073-y2003 EQ 1)
V_dih = Sum_dih{V_n/2¥([1 + cos(n*phi  -gamma))}

In the gromacs manual Opls V_dih is given in a different format
(eq. 4.59) which is missing the gamma term. The reference 51
jorgensen-JACS-v110-pp1657-1666-y1988
given in Gromacs User Manual does unfortunately NOT
have this V_dih spelled out.

Could someone clarify this?

Terveisin, Markus

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