Slater determinants, momentum density

The N-particle function (Pq e lA y ) is given, in general as a linear combination of Slater determinants constructed from plane waves, thus extending the treatment of both Macke [53, 54] and of March and Young [55]. Thus, we have < o = IxC/cXx. where Xk is the Slater determinant y = (JV) det [( li,..., and < ij,(r) is the plane wave defined in Eq. (1), with momentum e Z. Clearly, in view of this definition of o 6 the resulting density is... 

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