Molecular orbitals united atom notation

We have placed special emphasis on using a consistent notation throughout the book. Since quantum chemists use a number of different notations, it is appropriate to define the notation we have adopted. Spatial molecular orbitals (with latin indices ij, k...) are denoted by These are usually expanded in a set of spatial (atomic) basis functions (with greek indices ju, V, A,...) denoted by 0. Molecular spin orbitals are denoted by x Occupied molecular orbitals are specifically labeled by a, b, c,... and unoccupied (virtual) molecular orbitals are specifically labeled by r, s, r,... Many-electron operators are denoted by capital script letters (for example, the Hamiltonian is Jf), and one-electron operators are denoted by lower case latin letters (for example, the Fock operator for electron-one is /( )). The exact many-electron wave function is denoted by O, and we use T to denote approximate many-electron wave functions (i.e., the Hartree-Fock ground state wave function is o while FS is a doubly excited wave function). Exact and approximate energies are denoted by S and , respectively. All numerical quantities (energies, dipole moments, etc.) are given in atomic units. 

Some texts define A as identical to m.) Similar to the s,p, d,/notation for hydrogen-atom states, a letter code is used to specify A, the absolute value (in atomic units) of the component along the molecular axis of the electron s orbital angular momentum ... 

---