Multireference configuration interaction wave functions

Derivatives from Multireference Configuration Interaction Wave Functions 

We consider a multireference Cl (MRCI) wave function calculated from a set of MCSCF orbitals. The Cl reference state is denoted by CI at X0 and by CI(g) at the displaced geometry X0 + g. In addition to the reorthonormalization part, the MRCI orbital connection contains the MCSCF orbital 

The set of states k constitutes an orthonormal basis for the orthogonal complement to CI . 

The geometry dependence of the P parameters is obtained from the requirement that the total energy in Eq. (Ill) must be stationary in the perturbed field 

The parameters P may be expanded in a power series in the nuclear displacement 

---

Figure 2. (rel) = AEf2 and C(nonrel) = AE12.A, iiA, at each iteration of the solution of Eq. (15b) for OH + H2 using multireference configuration interaction wave functions. 

Jeziorski B, Paldus J (1990) Valence universal exponential ansatz and the cluster structure of multireference configuration interaction wave function. J Chem Phys 90 2714-2731... 

IV. Derivatives from Multireference Configuration Interaction Wave Functions... 

N. GUka, P. R. Taylor, C. M. Marian. Electron spin-spin coupling from multireference configuration interaction wave functions. J. Chem. Phys., 129 (2008) 044102. 

D. E. Woon andT. H. Dunningjr.,/. Chem. Phys., 99,1914 (1993). Benchmark Calculations with Correlated Molecular Wave Functions. I. Multireference Configuration Interaction Calculations for the Second Row Diatomic Hydrides. 

This calculation is typically performed in some form of a restricted configuration interaction (Cl) expansion (CASSCF [complete active space self consistent field], MRCI [multireference configuration interaction]). The perturbation V is represented by the operators and The perturbed wave function F and energy E satisfy the equation... 

Multireference configuration interaction (MRCI) calculations based on valence complete active space self-consistent field (CASSCF) wave functions with the quadruples corrections (-I-Q) [25-30] were used to determine the excitation energies of the N and P atoms using the AVQZ basis set. 

The MCSCF provides a good first-order description covering the static electron correlation due to degeneracy problems. Dynamic electron correlation should be addressed with the MCSCF wave function as a reference. The multireference configuration interaction, or MRCI, generates excited determinants from all (or selected) determinants included in the MCSCF. The complete active space perturbation theory, second order (CASPT2) is a more economical approach. Both methods can be applied to compute excited states. 

Initially only state-averaged multiconfigurational self-consistent field (SA-MCSCF) wave functions could be treated but subsequently the algorithm was extended to treat general multireference configuration interaction (MRCI) wave functions. Here x(X) denotes the space fixed frame coordinates of the A electrons nuclei) and < >/ is one of A electronic... 

Engels B (1994) A detailed study of the configuration selected multireference configuration-interaction method combined with perturbation-theory to correct the wave-function. J Chem... 

Benchmark calculations with correlated wave functions. I. Multireference configuration interaction calculations for the second-row diatomic hydrides , D. E. Woon and T. H. Dunning, Jr., J. Chem. Phys.,... 

The adiabatic electronic states, equation (2), are approximated by multireference configuration interaction (Cl) wave-functions, expanded in a configuration state fiinction (CSF) basis ... 

---