User documentation for the HQS Spin Mapper

This is the user documentation for the HQS Spin Mapper package.

The intended purpose of HQS Spin Mapper is the investigation of first-principles Hamiltonians of real input materials for orbitals of spin-like character. The implemented scope allows for both solids and molecules as input materials. Once orbitals of spin-like characters have been identified, an effective spin-bath model description can be derived for this material. Here the spin-bath model is a system of spins embedded in a material-specific fermionic environment (or bath).

A potential use case is the study of materials with dominant spin physics (i.e. magnetism) on a quantum computer. For this purposes HQS Spin Mapper provides a method to derive an accurate material-specific effective spin-bath model description from first principles, which can be used in a computation on a quantum device.

The figure above shows schematically the high-level procedure.

1. In the first step, the basis orbitals of spin-like character is identified based on their local parity. This local parity is obtained from the 1-RDM and 2-RDM, which are computed using correlated ab-initio methods (e.g. MP2/CCSD/CASSCF/...).

2. Secondly, mapping of the original Hamiltonian to a spin-bath model is performed by utilizing the generalized Schrieffer-Wolff transformation.

For a detailed description of the full workflow please refer to the Theoretical background chapter.

Glossary