Real-space pseudopotential methods for calculating the vibrational Stark tuning rate

We introduce a real-space method based on pseudopotentials constructed within density functional theory for computing the vibrational Stark effect. With wave functions defined in real space and cluster boundary conditions, convergence is controlled solely by the grid spacing. Moreover, charged systems can be incorporated without a compensating background charge. Real space methods also have the advantage that neither polarization functions nor supercells are required to simulate external electric fields. We illustrate this method by calculating the Stark tuning rates of small carbonyls and nitriles. The use of high-order integration techniques allow for a coarser (less expensive) grid spacing. Perturbative methods for determining the tuning rate will also be discussed.