Wednesday, March 27, 2013

NMR shielding constants through polarizable embedding

After I finished my Ph.D. in the Jan Jensen group, I've begun working at the University of Southern Denmark with Jacob Kongsted.

Apart from using DALTON instead of GAMESS I've also switched gears and I am now focused on an advanced form of QM/MM which is called polarizable embedding (see this paywalled link for details). Basically your gas-phase Fock operator is extended with interactions from the surroundings. In the language of polarizable embedding (PE) we constructs the effective Fock operator here for Hartree-Fock

$\hat{f}_{eff} = \hat{f}_{HF} + \hat{\nu}_{PE}$

The PE is a sum of interactions from the surroundings onto a molecule of interest. I will deal with the specifics of the PE approach later on.

This is all fine and dandy, but until now the PE model has focused solely on electronic molecular properties. I've extended it so you can calculate nuclear magnetic shielding constants in the PE model using London atomic orbitals (you might know them as Gauge-Including Atomic Orbitals) with contributions from charges, dipoles (induced and static) and quadrupoles. The hope is that we need a small QM region due to a very high-quality potential compared to previous QM/MM studie (see here for an example of needed more than 1000 atoms for converged NMR shieldings).

We'll see how it goes.