A package for nonadiabatic chemistry in diabatic representation

The core of diabatic representation is its constant basis vectors. The most amazing property derived from this core is perhaps the equivalence between an operator and its matrix form in diabatic representation. Consider an operator A, whose diabatic matrix form is Ad:

• Applying Ad to wave function vector is isomorphic to applying A to wave function, of course
• ▽Ad equals to the diabatic ▽A matrix. In general representations, however, you need another term accounting for the gradient of basis vectors

In quantum mechanics a representation is usually defined to diagonalize some operator, e.g. adiabatic representation diagonalizes electronic Hamiltonian operator. That can become problematic, however, when the operator has (near) degenerate eigen values, since the corresponding eigen vectors can arbitrarily mix, introducing singularity to the gradient of basis vectors

For detailed theories, see theory.md

We version diabatz with x.y.z format, where:

• x stands for major version, e.g. model change
• y stands for minor version, e.g. loss change
• z stands for patch version, e.g. optimizer change