In collaboration with Laura Ratcliff and Dr Nicholas Hine
The method implemented in ONETEP optimizes local orbitals to
minimize the total energy. This does a very good job of
describing the occupied electronic states that contribute to the
total energy, but fails to capture the unoccupied states that
are important for calculating spectra. We have devised a new
algorithm for optimizing a second set of local orbitals to
describe these unoccupied electronic states, form which optical
absorption spectra may be calculated in excellent agreement
with conventional DFT methods.