# Two-electron states of a group V donor in silicon from atomistic full configuration interaction

## TL;DR

This paper introduces an atomistic full configuration interaction method to accurately model two-electron states in silicon donors, capturing complex exchange and correlation effects crucial for quantum computing applications.

## Contribution

The work develops a comprehensive atomistic CI approach that incorporates silicon's full bandstructure and atomic details, providing new insights into donor electron states and their control.

## Key findings

- Excited s-like states significantly affect donor charging energy.
- Triplet states emerge under certain electric fields, indicating tunable spin states.
- Calculated exchange energies suggest potential for spin control in quantum devices.

## Abstract

Two-electron states bound to donors in silicon are important for both two qubit gates and spin readout. We present a full configuration interaction technique in the atomistic tight-binding basis to capture multi-electron exchange and correlation effects taking into account the full bandstructure of silicon and the atomic scale granularity of a nanoscale device. Excited $s$-like states of $A_1$-symmetry are found to strongly influence the charging energy of a negative donor centre. We apply the technique on sub-surface dopants subjected to gate electric fields, and show that bound triplet states appear in the spectrum as a result of decreased charging energy. The exchange energy, obtained for the two-electron states in various confinement regimes, may enable engineering electrical control of spins in donor-dot hybrid qubits.