Complex-valued natural orbitals in electron wavepacket dynamics

3 Complex-valued natural orbitals in electron wavepacket dynamics 

The natural orbitals, which are eigenfunctions of the first order density matrix, are among the well-known quantities in standard quantum chemistry. However, the natural orbitals resulting from a time-dependent electronic wavefunction such as SET and PSANB are complex-valued in general, and 

Equation (7.17) does not determine the phase of the natural orbital. It is necessary, therefore, to fix the phase factor so that the real part of has the largest norm. 

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