Generates one-body positivity constraints on fermionic RDMs.

The specific constraints implemented are known positivity constraints
on the one-fermion reduced density matrices. Constraints are generated
in the form of FermionOperators whose expectation value is known to be
zero for any N-Representable state. Generators are used for efficiency.

n_orbitals int

number of spin-orbitals on which operators act.

n_fermions int

number of fermions in the system.

Constraint is a FermionOperator with zero expectation value.