I would like to study the energy change due to the inclusion of a chlorine group. However, I got a huge induction energy and eventually a positive sapt0 energy. Using the Huckel guess as well as other tricks (i.e. soscf) as sugessted by this post does not help. (Unbelievable induction energy in SAPT0 - #4 by hokru)
Below is my output file. The cc-pvtz-pp basis set for Mo is used for the cc-pVTZ-minao basis set.
Many thanks for your help.
2-chloroallyl.mpi4.out.txt (75.2 KB)
The huge induction energy and the large positive SAPT0 energy are (I think) resultant of how the monomers are chosen. In the whole molecule, the chlorine atom seems to be bonded to a carbon atom (C9). The interaction energy between this chlorine atom and the “other monomer” will then necessarily include what appears to be a covalent bond, and SAPT is essentially guaranteed to fail when monomers are covalently bound (or more generally, if the atoms on different monomers are so close to one another).
Though, the induction energy is so off that it seems something else is also going on there.
Thank you for your help. But I thought the fisapt is capable to cut a sigma bond, isnt it?
Consider a molecule made up of three fragments linked like A-C-B, where each dash is a sigma bond. For example, in 2-aminophenol, fragment C could be the aromatic ring, fragment A could be the hydroxyl substituent, and fragment B could be the amino substituent.
F/I-SAPT can tell you:
- for two molecules, the contribution to the total noncovalent interaction energy associated with the pairwise interaction between A or B on the first molecule and A or B on the second molecule
- within the same molecule, the noncovalent interaction energy between fragments A and B in the embedding field of fragment C that links them.
F/I-SAPT cannot tell you:
- within the same molecule, the noncovalent interaction energy between fragment A and the rest of the molecule or between fragment B and the rest of the molecule. As Jeff said above, this interaction is mediated through a covalent bond. SAPT is a perturbation theory method that knows about electrostatic interactions, dispersion, etc. but doesn’t know about bonding orbitals. SAPT will fail to describe this interaction.
- any interaction energy when any of the fragments A, B, or C are a single atom. The localization procedure used in F/I-SAPT generally works well for functional groups but fails for single atoms. There may be exceptions to this, but generally the fragments need to be larger than a single atom.