An Ansatz abstract type contains all the metadata that defines a wavefunction approximation.
For example, if we create a FCIAnsatz subtype, then this contains the metadata
needed to diagonalize the Hamiltonian in the FCI basis.
Diagonalization of H in a RASCI determinant basis would then require a different
subtype, one that specified orbital spaces and such.
Since an Ansatz essentially defines a Slater determinant basis,
the combination of an Ansatz, and an InCoreInts object can fully define
the action of the operator (defined by the integrals) on a trial state
(defined by the Ansatz). This is simply a LinearMap, provided by the LinearMaps packages.
A LinearMap simply implements the action of our Hamiltonian on a trial state
defined by the Ansatz. By pairing this LinearMap with a Solver concrete
subtype, we can then generate our solution, which is a Solution{P,T} type.
A Solution{P,T} is then essentially a set of eigenstates for Ansatz, P, of
datatype T. This can then be used for constructed RDMs and operator matrices,
as we wish to do in FermiCG.
solve(Ansatz + InCoreInts + SolverSettings) --> Solution --> RDMs and Operators
AnsatzFCIAnsatzRASCIAnsatz- ...
# get h0, h1, h2 from pyscf or elsewhere and create ints
ints = InCoreInts(h0, h1, h2)
# to use FCI, we simply need to define the number of orbitals and electrons
ansatz = FCIAnsatz(norb, n_elec_a, n_elec_b)
# We define some solver settings - default uses Arpack.jl
solver = SolverSettings(nroots=3, tol=1e-6, maxiter=100)
# we can now solve our Ansatz and get energies and vectors from solution
solution = solve(ints, ansatz, solver)
display(solution)
e = solution.energies
v = solution.vectors
# This solution can then be used to compute the 1RDM
rdm1a, rdm1b = compute_1rdm(solution, root=2)# get h0, h1, h2 from pyscf or elsewhere and create ints
ints = InCoreInts(h0, h1, h2)
# to use RASCI, we need to define the number of orbitals, electrons, number of orbitals in each RAS subspace (ras1, ras2, ras3), maximum number of holes allowed in ras1, and maximum number of particle excitations allowed in ras3
ansatz = RASCIAnsatz(norb, n_elec_a, n_elec_b, (norbs_ras1, norbs_ras2, norbs_ras3), max_h=n_holes, max_p=n_particles)
# We define some solver settings - default uses Arpack.jl
solver = SolverSettings(nroots=3, tol=1e-6, maxiter=100)
# we can now solve our Ansatz and get energies and vectors from solution
solution = solve(ints, ansatz, solver)
display(solution)
e = solution.energies
v = solution.vectors
# This solution can then be used to compute the 1RDM
rdm1a, rdm1b = compute_1rdm(solution, root=2)