[gmx-users] Question about OPLS atomtypes
adeyoung at andrew.cmu.edu
Mon Nov 5 20:12:21 CET 2012
If you have time, I have a question about the OPLS parameters given in the
files located in the "top" directory (for example,
In the oplsaa.ff directory, there is a file atomtypes.atp. At the top of
this file, it says:
; Types 1-134 are from the united-atom OPLS, which can be
; useful for solvents and/or CH2 optimizations (e.g. in lipids).
; Explicit all-atom parameters start with opls_135.
Is it true that there _could_ be all-atom parameters in Types 1-134, the
For example, I am trying to find parameters for carbon tetrachloride, CCl4.
I have found these possibilities in atomtypes.atp:
opls_122 12.01100 ; C CCl4
opls_123 35.45300 ; Cl CCl4
which, for example, have the following entries in ffnonbonded.itp:
opls_122 CT 6 12.01100 0.248 A 3.80000e-01 2.09200e-01
opls_123 Cl 17 35.45300 -0.062 A 3.47000e-01
Clearly, these entries each correspond to individual atoms, even though
opls_122 and opls_123 are in the "united-atom OPLS" section. I will be
describing the remainder of my system using all-atom OPLS parameters (CCl4
is just the solvent; I will also have solute); is it likely reasonably safe
to use the above parameters for C and Cl? In other words, I would be
"mixing" parameters from the united-atom and all-atom sections, because I
have been unable to find all-atom parameters for C and Cl in CCl4.
Carnegie Mellon University
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