ffsim.expectation_one_body_power¶
- ffsim.expectation_one_body_power(one_rdm, one_body_tensor, power=1)[source]¶
Expectation of power of one-body operator w.r.t. a Slater determinant.
A one-body operator \(O\) has the form
\[O = \sum_{pq} M_{pq} a_p^\dagger a_q.\]This function takes the matrix \(M\) as its first argument. Let \(\lvert \psi \rangle\) be the Slater determinant. Then this function returns the quantity
\[\langle \psi \rvert O^k \lvert \psi \rangle.\]- Note: Unlike most functions in ffsim, the inputs to this function are specified
in terms of spin-orbitals, not spatial orbitals. In other words, the one-rdm and the one-body tensors should have the same shape, and all orbitals are treated on an equal footing. The 1-RDM passed here should not be spin-summed, and the one-body tensors should be expanded when compared to the usual one-body tensors elsewhere in ffsim, i.e.,
scipy.linalg.block_diag(one_body_tensor, one_body_tensor).