I was following the FFTK tutorial using ORCA as a QM software to obtimize ethanol. the default route in FFTK during geometry optimization is MP2 6-31G* TightSCF opt. However, i read in this review article (Best-Practice DFT Protocols for Basic Molecular Computational Chemistry) that when doing geometry optimization other methods and basis sets are recommended such as B97-3c with a TZ basis set ( i used this one: def2-TZVP). Moreover, during charge optimization step i used the same method and basis set.
At the end, the partial charges produced was different from the tutorial and also different from CGENFF.
Is it correct to change the default function and basis set in FFTK?
Did you change both the method (from MP2 to DFT) and the basis set?
MP2 is more accurate than DFT,, yet it's more computationally expensive.
yes i changed both. I have read in the original paper of CGENFF that this selection of basis sets and methods is for the parameters to be compatible with the way charmm FF was parameterized
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