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  • Electronic Resource  (2)
  • Electron correlation  (1)
  • Inorganic Chemistry  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical chemistry accounts 97 (1997), S. 331-340 
    ISSN: 1432-2234
    Keywords: Key words: Gradients ; Perturbation theory of electronic structure ; MP2 ; Electron correlation ; Coulomb interaction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract. The evaluation of RI-MP2 first derivatives with respect to nuclear coordinates or with respect to an external electric field is described. The prefix RI indicates the use of an approximate resolution of identity in the Hilbert space of interacting charge distributions (Coulomb metric), i.e., the use of an auxiliary basis set to approximate charge distributions. The RI technique is applied to first derivatives of the MP2 correlation energy expression while the (restricted) Hartree-Fock reference is treated in the usual way. Computational savings by a factor of 10 over conventional approaches are demonstrated in an application to porphyrin. It is shown that the RI approximation to MP2 derivatives does not entail any significant loss in accuracy. Finally, the relative energetic stabilities of a representative sample of closed-shell molecules built from first and second row elements have been investigated by the RI-MP2 approach, and thus it is tested whether such properties that refer to potential energy hypersurfaces in a more global way can be described with similar consistency to the more locally defined derivatives.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 621 (1995), S. 258-286 
    ISSN: 0044-2313
    Keywords: Structures of phosphorus (amorphous, red, white, Hittorf, cluster, allotrope, phosphane, phosphide) ; ab initio calculations ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Theoretische Untersuchung der strukturellen Systematik kovalenter PhosphorgerüsteAufbauend auf Arbeiten von Baudler wird eine Heuristik zur systematischen Herleitung und Klassifizierung kovalenter Phosphorgerüststrukturen in polycyclischen Phosphanen, phosphorreichen Phosphiden und Elementstrukturen des Phosphors (mit Ausnahme der schwarzen Allotrope) eingeführt. Von dieser Systematik geleitet werden mit Ab-initio-Methoden noch unbekannte molekulare oder makromolekulare Formen vor allem des elementaren Phosphors untersucht und mit Hittorfschem Phosphor und mit P4 verglichen. Das Auftreten der letztgenannten Elementstrukturen wird erklärt, die mögliche Existenz einer weiteren kristallinen allotropen Form bestätigt und die wahrscheinliche Struktur des amorphen (roten) Phosphors diskutiert. Insgesamt erschließt die vorgestellte Kombination von chemischer Heuristik mit umfangreichen Ab-initio-Rechnungen ein zusammenhängendes Verständnis von Energetik und Aufbau kovalenter Strukturen (nicht nur) des elementaren Phosphors.
    Notes: Starting from earlier work by Baudler we introduce a chemical heuristic for the systematic deduction and classification of covalent partial structures of phosphorus in polycyclic phosphanes, phosphorus-rich polycyclic phosphides, and allotropes of phosphorus except the black forms. This approach is used to direct ab initio techniques (which also confirm the rules) in the quest for as yet unknown forms of molecular or macromolecular phosphorus. Based on calculated stabilities of systematically generated structural alternatives we rationalize the stabilities of Hittorf's phosphorus and of molecular P4, confirm the possible existence of at least one other crystalline allotropic form of phosphorus, and provide insight into the probable structure of amorphous red phosphorus. In total, the combined approach of chemical heuristics and large scale ab initio calculations presented in this work supplies a coherent chemical understanding of covalent polyphosphorus structures.
    Additional Material: 17 Ill.
    Type of Medium: Electronic Resource
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