Hi Matt,

I have been trying to define the MPO for electron number operators following the definition of the Hamiltonian MPO:

```
function ITensorInfiniteMPS.unit_cell_terms(::Model"eNumber")
opsum = OpSum()
opsum += "Ntot", 1
return opsum
end
NumberOp = InfiniteSum{MPO}(Model("eNumber"), s)
```

However, I got the error “LoadError: MethodError: no method matching translatecell(::ITensorInfiniteMPS.var”#_shift_cell#149"{Int64}, ::Scaled{ComplexF64, Prod{Op}}, ::Int64)".

Another related question is how do we calculate the electron correlation functions in VUMPS? Is there a documentation or example that I could refer to?

Thanks again for your time,

-Meng