# Density matrix in Momentum Space

1. Apr 14, 2013

### Morberticus

I have an one-body density matrix in a Sine wave basis set (Thus psi = psi*). Unfortunately, these are not the natural orbitals (I have correlated particles), so I have off-diagonal elements. I believe I know how to extract the charge density from this density matrix

$\rho(x;x') = \sum_{ij} c_{ij}\psi_i(x)\psi_j(x')$

Where x' = x. Can I do something similar to extract a "momentum density"?

$\rho(k;k') = \sum_{ij} c_{ij}\psi_i(k)\psi_j(k')$

Where k' = k?

Thanks