[ghemical-devel] Re: RM1 parameterization in MOPAC?

[Geoffrey Hutchison]

I recently ran across an article on the new "RM1" semiempirical  
model. Basically, a group from Brazil found a better parameterization  
for AM1 -- same model, same number of parameters. Just the parameters  
changed. The result is generally better, except slightly worse on  
bond and dihedral angles than AM1. But heat of formation, dipole  
moment, ionization potential (i.e., HOMO energy) and bond lengths are  
all better.

RMI: A reparameterization of AM1 for H, C, N, O, P, S, F, Cl, Br, and I
by Rocha GB, Freire RO, Simas AM, et al.
http://dx.doi.org/10.1002/jcc.20425

Conveniently, the supplemental information includes a file formatted  
for MOPAC "EXTERNAL" keyword, e.g.

AM1 GNORM=0.01 SCFCRT=1.D-8 EXTERNAL=RM1.rm1

(WARNING)
> Whenever you use AM1 EXTERNAL=RM1.rm1, please make sure that your  
> molecule does not contain any atoms other than H, C, N, O, P, S, F,  
> Cl, Br, and I; otherwise there will be a mix of RM1 with AM1  
> parameters, which will render the calculation meaningless.

I'm attaching the RM1.rm1 file -- if anyone would like to try it out  
with MOPAC7, it might be interesting. Perhaps a new version of  
Ghemical can add "RM1" to the list of calculation options and use the  
external parameter file.

Cheers,
-Geoff
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