Configuration-interaction theory electronic gradient

Shepard R (1995) The analytic gradient method for configuration interaction wave functions. Yarkony DR (ed) In Modern electronic structure theory part I, World Scientific, Singapore, p 345... 

Density-Functional Theory. Transition metals pose a problem for classical quantum chemical methods like self-consistent field (SCF), perturbation theory, configuration interaction (Cl), and variations on these methods, because of the very large electron correlation. SCF underestimates binding substantially, and post-SCF methods are so expensive for transition metals that one can do a calculation only on models with few atoms. DFT on the other hand is relatively cheap it is about as expensive as SCF. Moreover, with the development of the generalized-gradient approximations it is also reasonably accurate. A large majority of quantum chemical... 

In spite of the impressive progress which has been achieved with conventional ab-initio methods as the Configuration-Interaction or Coupled-Cluster schemes in recent years density functional theory (DFT) still represents the method of choice for the study of complex many-electron systems (for an overview of DFT see [1]). Today DFT covers an enormous variety of fields, ranging from atomic [2,3], cluster [4,5] and surface physics [6,7] to the material sciences [8-10]. and theoretical biophysics [11-13]. Moreover, since the introduction of the generalized gradient approximation DFT has become an accepted method also for standard quantum chemical applications [14,15]. Given this tremendous success of nonrelativistic DFT the question for a relativistic extension (RDFT) arises quite naturally in view of the large number of problems in which relativistic effects play an important role (see e.g. Refs.[16,17]). 

To obtain errors of 1 kcal/mol or better, it is essential to treat many-body effects accurately and, we believe, directly. Although commonly used methods such as the density functional theory within the local density approximation (LDA) or the generalized gradient approximation (GGA) may get some properties correctly, it seems unlikely that they, in general, will ever have the needed precision and robustness on a wide variety of molecules. On the other hand, methods that rely on a complete representation of the many-body wavefunction will require a computer time that is exponential in the number of electrons. A typical example of such an approach is the configuration interaction (Cl) method, which expands the wavefunction in Slater determinants of one-body orbitals. Each time an atom is added to the system, an additional number of molecular orbitals must be considered, and the total number of determinants to reach chemical accuracy is then multiplied by this factor. Hence an exponential dependence of the computer time on the number of atoms in the system results. 

Basis Sets Correlation Consistent Sets Benchmark Studies on Small Molecules Complete Active Space Self-consistent Field (CASSCF) Second-order Perturbation Theory (CASPT2) Configuration Interaction Configuration Interaction PCI-X and Applications Core-Valence Correlation Effects Coupled-cbister Theory Density Functional Applications Density Functional Theory (DFT), Har-tree-Fock (HF), and the Self-consistent Field Density Functional Theory Applications to Transition Metal Problems Electronic Structure of Meted and Mixed Nonstoi-chiometric Clusters G2 Theory Gradient Theory Heats of Formation Hybrid Methods Metal Complexes Relativistic Effective Core Potential Techniques for Molecules Containing Very Heavy Atoms Relativistic Theory and Applications Semiempiriced Methetds Transition Metals Surface Chemi-ced Bond Transition Meted Chemistry. 

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