A Theoretical Investigation of the Nitrogen-Vacancy Center in Diamond as a Single Molecule Sensor and Qubit

Abstract:
Charged defects are traditionally computed by adding/subtracting
electrons for negative/positive impurities. When using periodic
boundary conditions, this results in artificially charged supercells
that require a compensating background charge of the opposite sign,
which makes slab supercells problematic because of an arbitrary
dependence on the vacuum thickness. In this work, we test the method of
using neutral supercells through the use of a substitutional electron
donor (acceptor) to describe charged systems. We use density functional
theory (DFT) to compare the effects of charging the well-studied
NV-center in diamond by a substitutional donor nitrogen. First, we
investigate the influence of the donor-N on the NV-center properties
as a function of the distance between them, and find that they converge
toward those obtained when adding an electron. We analyze the spin
density and conclude that the donor-N has a zero magnetic moment, and
thus, will not be seen in electron spin resonance. We validate our DFT
energies through comparison to GW simulations.

Using our new method of charging by explicit electron donors/acceptors,
we investigate a number of situations: a) NV-center in vicinity
to a terminated surface, b) NV-center in vicinity to an intrinsic
stacking fault, c) NV-center in vicinity to an additional, neutral
nitrogen, d) charging other defects in diamond, besides the NV-center.
We find that the NV-center can be very close (5 Å) to terminated
surfaces and intrinsic stacking faults without being greatly affected,
which is tremendously beneficial for the sensing applications. We also
find that a nearby neutral nitrogen does not have a large effect on the
NV-center, which is also beneficial, as many diamonds tend to have
large densities of nitrogen. Finally, our method also works for
charging other defects in diamond. This opens up the way to use our
method in other materials and situations.