Quantum Numbers

When MECI is used, the output contains information on the symmetry of each state. States of different symmetries are automatically orthogonal, but states of the same symmetry do not need to be orthogonal. Of course they are orthogonal, and, to emphasize this fact, an extra symmetry label is added. This label is, in fact, a quantum number, and is given under the heading "Q.N." in the output. The first occurrence of a given irreducible representation is given the Q.N. "1", the second, "2", etc. By using the Q.N. and the symmetry label, each state can be assigned a unique label.