Εξειδίκευση τύπου :	Άρθρο σε επιστημονικό περιοδικό
Τίτλος:	State- and Property-Specific Quantum Chemistry: Basic Characteristics, and Sample Applications to Atomic, Molecular, and Metallic Ground and Excited States of Beryllium
Δημιουργός/Συγγραφέας:	[EL] Νικολαΐδης, Κλεάνθης A.[EN] Nicolaides, Cleanthes A.
Εκδότης:	John Wiley & Sons, Inc.
Τόπος έκδοσης:	MALDEN
Ημερομηνία:	2011-11-05
Γλώσσα:	Αγγλικά
ISSN:	0020-7608
DOI:	10.1002/qua.23106
Περίληψη:	Many problems in Atomic and Molecular Physics can be understood conceptually and quantitatively by using symmetry-adapted, state-specific wavefunctions whose computation is geared so as to account for at least those parts which describe reliably the characteristics of closed-and open-(sub)shell electronic structures that contribute overwhelmingly to the property or phenomenon of interest. If additional terms in the wavefunction are required by the problem, this is feasible via methods of configuration-interaction or low-order perturbation theory. This is the main argument of the state- and property-specific approach (SPSA) to Quantum Chemistry. In this framework, the aim is to obtain the state wavefunction, Psi(n), in the form a(0)Psi(0)(n) + Phi(corr)(n), where a(0) approximate to 1. Psi(0)(n) is a state-specific zero-order description of ground and excited states of the discrete as well as of the continuous spectrum. In general, it is multiconfigurational and its construction follows from the "Fermi-sea" set of orbitals. The Psi(0)(n) is used as reference for analysis and/or for further improvement of the overall calculation, if necessary. The level of accuracy of the computation of the remaining Phi(corr)(n) depends on the property under investigation. The arguments are supported by characteristic examples on ground and excited states of atomic, molecular and metallic Beryllium. Some of these SPSA results are compared with results from more conventional methods of electronic structure. Special attention is given to the weak bond of the Be(2) X(1)Sigma(+)(g) state, which has attracted the interest of quantum chemists for decades. By asserting that the formation of the bond at about 2.5 angstrom is influenced by the interactions involving excited states, I point to the corresponding significance in zero-order ("Fermi-sea") not only of p-waves but also of d-waves whose origin is in the valence-Rydberg state mixing of the lowest (1)D and (1)P(o) states of Be. Therefore, the "Fermi-sea" ("active space") is represented by the Be set of {2s,2p,3s,3p,3d} orbitals. The initially heuristic predictions are supported by calculations (using the MOLPRO code) of the lowest seven Be(2)(1)Sigma(+)(g) states, whose Psi(0)(n) are obtained at the state-averaged complete active space self-consistent field level. These results are verified by the computation of a(0)Psi(0)(n) + Phi(corr)(n) at the MRCISD level, where indeed a(0) approximate to 1 over the whole potential energy curve. This type of analysis and the corresponding results imply that by a properly justified choice of the zero-order orbital set, the origin of the Be(2) bond is to be found in "nondynamical" - type correlations. This conclusion differs from that of Schmidt et al. [J Phys Chem A, 2010, 114, 8687], who argued that the formation of the Be(2) weak bond should be attributed exclusively to "dynamical" correlations that are defined with respect to the [2s,2p] "active space" associated with the Be (1)S ground state.
Τίτλος πηγής δημοσίευσης:	International Journal of Quantum Chemistry
Τόμος/Κεφάλαιο:	111
Τεύχος:	13
Σελίδες:	3347-3361
Θεματική Κατηγορία:	[EL] Χημεία (Γενικά)[EN] Chemistry (General) [EL] Φυσική[EN] Physics [EL] Μαθηματικά[EN] Mathematics
Λέξεις-Κλειδιά:	quantum chemistry state-specific theory of electronic structures excited states electron correlation Be (1)S molecule Chemistry, Physical Mathematics, Interdisciplinary Applications Physics, Atomic, Molecular & Chemical
Αξιολόγηση από ομότιμους (peer reviewed):	Ναι
Κάτοχος πνευματικών δικαιωμάτων:	© 2011 Wiley Periodicals, Inc. Int J Quantum Chem 111: 3347-3361, 2011
Ηλεκτρονική διεύθυνση περιοδικού (link) :	http://www.interscience.wiley.com/jpages/0020-7608
Σημειώσεις:	Special Issue SI
Εμφανίζεται στις συλλογές:	Ινστιτούτο Θεωρητικής και Φυσικής Χημείας (ΙΘΦΧ) - Επιστημονικό έργο