THEORETICAL STUDY OF SPIN DEFECTS WITH AN HUBBARD MODEL COMBINED WITH DENSITY FUNCTIONAL THEORY CALCULATIONS

Crystal point defects offer one possible pathway towards the solid-state implementation of quantum applications like nanoscale sensors for magnetometry or thermometry, single photon emission, or qubits for quantum computing. Conditions for such applications are that the defect has a high spin state in the ground state, a long spin lifetime (coherence) time which characterizes the timescale on which the spin retains its polarization (phase), and offers the possibility to manipulate the spin state by optical excitations and to control it with magnetic, electric or strain fields.

In the present work, we combine first-principle generalized DFT calculations with an in-house extended Hubbard model to describe the defect many-body energy states of some points defects. Using DFT and the ΔSCF method, we performed calculations of the ground state and of some excited states total energies, which we used to parameterize our Hubbard model. We apply our methods to the case of the negatively charged nitrogen-vacancy center, computed with DFT-HSE06, as well as to the to the carbon-vacancy-carbon complex in alpha boron, computed with DFT-GGA.