  The Stark shift of the hyperfine coupling constant is investigated for a P
donor in Si far below the ionization regime in the presence of interfaces using
Tight-binding and Band Minima Basis approaches and compared to the recent
precision measurements. The TB electronic structure calculations included over
3 million atoms. In contrast to previous effective mass based results, the
quadratic Stark coefficient obtained from both theories agrees closely with the
experiments. This work represents the most sensitive and precise comparison
between theory and experiment for single donor spin control. It is also shown
that there is a significant linear Stark effect for an impurity near the
interface, whereas, far from the interface, the quadratic Stark effect
dominates. Such precise control of single donor spin states is required
particularly in quantum computing applications of single donor electronics,
which forms the driving motivation of this work.
