From: Vermaas, Josh (
Date: Wed Apr 24 2024 - 08:35:29 CDT

Hi Joel,

What basis set was successful? The rest of CHARMM36 uses HF/6-31G(d), and there are some other assumptions in parameterization that depend on this basis set. Like the multiplier by 1.16 between QM and MM energies is strictly empirical, and probably won't extend to other basis sets. If you are using some semi-empirical method, that probably won't be very compatible with the assumptions built into the CHARMM parameterization scheme, but if its still the HF method with a bigger basis set, that is probably fine.


On 4/24/24 07:37, Joel Subach wrote:
....and the ffTK default ORCA Base Set is: ! MP2 6-31G* TightSCF opt

On Wed, Apr 24, 2024 at 12:07 PM Joel Subach <<>> wrote:
 Hello VMD Forum,

Towards the above topic, I have been executing the ffTK Tutorial suggested QM Base Set, however, upon reaching the QM generated Hessian Output the above base set has generated errors, accordingly I have instead executed an ORCA Forum suggested Base Set which is so far executing successfully.

Would ffTK regardless suggest the ffTK Tutorial Base Set if functioning in lieu of other Base sets since the HF/6-31G(d) level of theory is to maintain the consistency with the CHARMM force field?

Thanks if you know since if not to the above then I may go back and use the ORCA Tutorial to modify each Base Set accordingly.


Josh Vermaas<>
Assistant Professor, Plant Research Laboratory and Biochemistry and Molecular Biology
Michigan State University