# 5.3.7 Semi-Empirical Functionals

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 (Z = 37) to Xe (Z = 54), def2-ECP has to be used.938

• 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 (Z = 37) to Rn (Z = 86), def2-ECP has to be used. It is a more accurate method than HF-3c as it has correlation.322

Example 5.4  Q-Chem input for HF-3c method.

$molecule 0 1 O -1.551007 -0.114520 0.000000 H -1.934259 0.762503 0.000000 H -0.599677 0.040712 0.000000 O 1.350625 0.111469 0.000000 H 1.680398 -0.373741 -0.758561 H 1.680398 -0.373741 0.758561$end

$rem JOB_TYPE = SP SCF_CONVERGENCE = 8 BASIS = MINIX METHOD = HF3C SCF_GUESS = SAD$end


Example 5.5  Q-Chem input for PBEh-3c method.

$molecule 0 1 O -1.551007 -0.114520 0.000000 H -1.934259 0.762503 0.000000 H -0.599677 0.040712 0.000000 O 1.350625 0.111469 0.000000 H 1.680398 -0.373741 -0.758561 H 1.680398 -0.373741 0.758561$end

$rem jobtype sp method PBEh-3c basis def2-mSVP xc_grid 000099000590 incdft 0 incfock 0 scf_convergence 8 thresh 14 symmetry false sym_ignore true$end