In the MCSCF method a multiconfiguration wavefunction is variationally optimized with respect to simultaneous variations of the orbitals and configuration coefficients. As explained in section 4.3, the Hartree-Fock wavefunction is uniquely defined by specifying the number of occupied orbitals in each symmetry and possibly the singly occupied orbitals. In the MCSCF case some more information is necessary. We will begin to explain the input for CASSCF (complete active space SCF), which is the simplest case.