  Developing devices that can reliably and accurately demonstrate the
principles of superposition and entanglement is an on-going challenge for the
quantum computing community. Modeling and simulation offer attractive means of
testing early device designs and establishing expectations for operational
performance. However, the complex integrated material systems required by
quantum device designs are not captured by any single existing computational
modeling method. We examine the development and analysis of a multi-staged
computational workflow that can be used to design and characterize silicon
donor qubit systems with modeling and simulation. Our approach integrates
quantum computational chemistry calculations with electrostatic field solvers
to perform detailed simulations of a phosphorus dopant in silicon. We show how
atomistic details can be synthesized into an operational model for the logical
gates that define quantum computation in this particular technology. The
resulting computational workflow realizes a design tool for silicon donor
qubits that can help verify and validate current and near-term experimental
devices.
