Calculation CASPT

In Table 14.8, we have listed the CASPT and MPPT energies calculated up to order 10 for the water molecule at the geometries / ref and 2/ ref- The CASPT results have been calculated using the uncontracted, determinantal scheme. In the CASPT calculations, a (3.0.1.2) valence CAS reference state is employed, with the inactive ai CAS orbital frozen in the MPPT calculations, the canonical lot Hartree-Fock orbital has been kept frozen. 

The other half of the isomerization takes place directly bypassing a trappable intermediate, as recently confirmed by extensive theoretical calculations [B3LYP, CASPT 2, (8/8)CASSCF] [145],... 

Although not rigorously size-extensive, CASPT behaves better than MRSDCI theory for systems of many electrons. The CASPT and other MRPT methods are important in the sense that they are the only generally applicable methods for ab initio calculations of dynamical correlation of open-shell and closed-shell multiconfigura-... 

---