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Bunge, Carlos F.  
Selected configuration interaction (SCI) for atomic and molecular electronic structure calculations is reformulated in a general framework encompassing all CI methods. The linked cluster expansion is used as an intermediate device to approximate CI coefficients BK of disconnected configurations (those that can be expressed as products of combinations of singly and doubly excited ones) in terms of CI coefficients of lowerexcited configurations where each K is a linear combination of configurationstatefunctions (CSFs) over all degenerate elements of K. Disconnected configurations up to sextuply excited ones are selected by Brownâ€™s energy formula, Î”EK=(EHKK)BK2/(1BK2), with BK determined from coefficients of singly and doubly excited configurations. The truncation energy error from disconnected configurations, Î”dis, is approximated by the sum of Î”EKS of all discarded Ks. The remaining (connected) configurations are selected by thresholds based on natural orbital concepts. Given a model CI space M, a usual upper bound ES is computed by CI in a selected space S, and EM=E S+Î”Edis+Î´E, where Î´E is a residual error which can be calculated by welldefined sensitivity analyses. An SCI calculation on Ne ground state featuring 1077 orbitals is presented. Convergence to within near spectroscopic accuracy (0.5 cm1) is achieved in a model space M of 1.4Ã— 109 CSFs (1.1 Ã— 1012 determinants) containing up to quadruply excited CSFs. Accurate energy contributions of quintuples and sextuples in a model space of 6.5 Ã— 1012 CSFs are obtained. The impact of SCI on various orbital methods is discussed. Since Î”Edis can readily be calculated for very large basis sets without the need of a CI calculation, it can be used to estimate the orbital basis incompleteness error. A method for precise and efficient evaluation of ES is taken up in a companion paper  
http://hdl.handle.net/2072/101673  
eng  
American Institute of Physics  
Tots els drets reservats  
AnÃ lisi dâ€™error (MatemÃ tica)
DinÃ mica molecular Estructura atÃ²mica Estructura electrÃ²nica NeÃ³ Atomic structure Electronic structure Error analysis (Mathematics) Molecular dynamics Neon 

Selected configuration interaction with truncation energy error and application to the Ne atom  
info:eurepo/semantics/article  
Recercat 