I am attempting to use a VQE algorithm to find the ground state of a deuterium nucleus by applying a constructed hamiltonian to an ansatz state with one parameter created by a circuit. While I am getting a different expectation value for different parameters, it does not line up with what I am supposed to get (from the paper I am attempting to replicate). I think the basis is wrong. How should I change the basis to fit the hamiltonian I am using? Should I change the basis of the hamiltonian (which I got from tensor products of pauli operators)? Or should I change the basis of the ansatz itself to fit that of the hamiltonian?
PS: https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.120.210501 this is the paper whose results I am trying to replicate (The H2 graph to be specific). They are using ↑ and ↓ as their basis while I am still on qiskit's default 0 and 1