Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Configuration interaction doubly excited

Equation [1] is an internally contracted configuration space, doubly excited with respect to the CAS reference function 0) = G4SSCF) one or two of the four indices p,q,r,s must be outside the active space. The functions of Eq. [1] are linear combinations of CFs and span the entire configuration space that interacts with the reference function. Labeling the compound index pqrs as (i or v, we can write the first-order equation as... [Pg.255]

The amount of computation for MP2 is determined by the partial transformation of the two-electron integrals, what can be done in a time proportionally to m (m is the number of basis functions), which is comparable to computations involved in one step of CID (doubly-excited configuration interaction) calculation. To save some computer time and space, the core orbitals are frequently omitted from MP calculations. For more details on perturbation theory please see A. Szabo and N. Ostlund, Modem Quantum Chemistry, Macmillan, New York, 1985. [Pg.238]

This is perhaps the easiest method to understand. It is based on the variational principle (Appendix B), analogous to the HF method. The trial wave function is written as a linear combination of determinants with the expansion coefficients determined by requiring that the energy should be a minimum (or at least stationary), a procedure known as Configuration Interaction (Cl). The MOs used for building the excited Slater determinants are taken from a Hartree-Fock calculation and held fixed. Subscripts S, D, T etc. indicate determinants which are singly, doubly, triply etc. excited relative to the... [Pg.101]

Notwithstanding, after hydrogen, helium is also the simplest naturally available atomic species, which, in contrast to one electron atoms, exhibits the additional electron-electron interaction, as a source of electronic correlations. Hence, helium is one of the simplest systems where electronic correlations can be studied. Direct manifestations of electronic correlations have been found, e.g., in doubly excited states of helium localized along highly asymmetric, though very stable, frozen planet configurations (FPC) (K. Richter et.al., 1990), or scarred by... [Pg.136]

A and B are the state symmetry species. The dotted parts of b and c are the potential curves for doubly excited cnfigu-rations. a describes the effect of configuration interaction... [Pg.73]

Configuration interaction (Cl) is conceptually the simplest procedure for improving on the Hartree-Fock approximation. Consider the determinant formed from the n lowest-energy occupied spin orbitals this determinant is o) and represents the appropriate SCF reference state. In addition, consider the determinants formed by promoting one electron from an orbital k to an orbital v that is unoccupied in these are the singly excited determinants ). Similarly, consider doubly excited (k, v,t) determinants and so on up to n-tuply excited determinants. Then use these many-electron wavefimctions in an expansion describing the Cl many-electron wavefunction [Pg.13]

In certain special cases the approximate symmetries in atoms are sufficiently well explained using the quasispin formalism. In particular, the quasispin technique can be utilized to describe fairly accurately configuration mixing for doubly excited states of the two-electron atom. In the quasispin basis the energy matrix of the electrostatic interaction operator of such configurations is nearly diagonal, and hence the quantum number of total quasispin Q is approximately good . [Pg.194]

CISD configuration interaction with singly and doubly excited determinants only DRE Dewar resonance energy... [Pg.35]


See other pages where Configuration interaction doubly excited is mentioned: [Pg.29]    [Pg.133]    [Pg.189]    [Pg.195]    [Pg.200]    [Pg.283]    [Pg.145]    [Pg.108]    [Pg.111]    [Pg.502]    [Pg.25]    [Pg.155]    [Pg.441]    [Pg.165]    [Pg.230]    [Pg.15]    [Pg.28]    [Pg.28]    [Pg.104]    [Pg.104]    [Pg.78]    [Pg.182]    [Pg.741]    [Pg.975]    [Pg.30]    [Pg.1047]    [Pg.73]    [Pg.30]    [Pg.363]    [Pg.230]    [Pg.189]    [Pg.195]    [Pg.1316]    [Pg.77]    [Pg.78]    [Pg.124]    [Pg.265]   
See also in sourсe #XX -- [ Pg.55 , Pg.57 , Pg.69 ]

See also in sourсe #XX -- [ Pg.55 , Pg.57 , Pg.69 ]




SEARCH



Configuration Interaction

Configuration interaction doubly excited configurations

Configurational interaction

Excited configuration

© 2024 chempedia.info