The following semi-empirical methods are available in Q-Chem:
HF-3c: It is an HF-based semi-empirical method which is used with a minimal basis called MINIX. All the elements from H to Xe are supported. For the elements from Rb () to Xe (), def2-ECP must be used.1100
PBEh-3c: It is a DFT based method which is used with def2-mSVP basis set.This is available for all the elements from H to Rn. For the elements from Rb () to Rn (), def2-ECP has to be used. It is a more accurate method than HF-3c as it has correlation,393 although the double- basis set makes it more expensive for large molecules.
Note: The HF-3c and PBEh-3c methods were parameterized for use with the aforementioned basis sets. Although Q-Chem does not enforce this, other basis sets should not be used unless there is a good reason for doing so, and only then with caution as the results may not match published accuracy.
$rem method hf-3c basis minix ecp def2-ecp $end $molecule -1 1 I 0.6539056222 0.0300979939 0.0000000000 O -2.8593081518 0.0835488510 0.0000000000 H -1.8947008157 0.2596704547 0.0000000000 H -2.8641221666 -0.8778240298 0.0000000000 $end
$molecule 0 1 O -1.551007 -0.114520 0.000000 H -1.934259 0.762503 0.000000 H -0.599677 0.040712 0.000000 O 1.350625 0.111469 0.000000 H 1.680398 -0.373741 -0.758561 H 1.680398 -0.373741 0.758561 $end $rem METHOD PBEh-3c BASIS def2-mSVP XC_GRID 000099000590 INCDFT 0 INCFOCK 0 SCF_CONVERGENCE 8 THRESH 14 SYMMETRY false SYM_IGNORE true $end