Computational Chemistry

9. Why is size-consistency in an ab initio method considered more important than
   variational behavior (MP2 is size-consistent but not variational)?


10. A common alternative to writing a Hartree–Fock wavefunction as an explicit
    Slater determinant is to express it using apermutation operatorP^which
    permutes (switches) electrons around in MOs. Examine the Slater determinant
    for a two-electron closed-shell molecule, then try to rewrite the wavefunction
    usingP^.

390 5 Ab initio Calculations