State-specific approach and computation of resonance states: Identification and properties of the lowest P-2(o) and D-2 triply excited states of He-

Nicolaides, CA; Piangos, NA

dc.contributor.author	Nicolaides, CA	en
dc.contributor.author	Piangos, NA	en
dc.date.accessioned	2014-03-01T01:51:20Z
dc.date.available	2014-03-01T01:51:20Z
dc.date.issued	2001	en
dc.identifier.issn	1050-2947	en
dc.identifier.uri	https://dspace.lib.ntua.gr/xmlui/handle/123456789/26264
dc.subject.classification	Optics	en
dc.subject.classification	Physics, Atomic, Molecular & Chemical	en
dc.subject.other	NEGATIVE-ION RESONANCES	en
dc.subject.other	AUTOIONIZING STATES	en
dc.subject.other	CONTINUOUS-SPECTRUM	en
dc.subject.other	MANY-ELECTRON	en
dc.subject.other	2-ELECTRON SYSTEMS	en
dc.subject.other	TIME-DEPENDENCE	en
dc.subject.other	BOUND-STATES	en
dc.subject.other	WIDTHS	en
dc.subject.other	HELIUM	en
dc.subject.other	THRESHOLD	en
dc.title	State-specific approach and computation of resonance states: Identification and properties of the lowest P-2(o) and D-2 triply excited states of He-	en
heal.type	journalArticle	en
heal.identifier.secondary	052505	en
heal.language	English	en
heal.publicationDate	2001	en
heal.abstract	We discuss aspects of the theory and computation of resonance (autoionizing) states of polyelectronic atoms and their positive and negative ions, in the context of the state-specific approach, using as paradigms the He(-)2s(2)2p P-2(o) and 2s2p(2) D-2 triply excited states. The He- D-2 resonance has been the subject of controversy about its nature and its very existence, with ramifications as to the physics of electron-He scattering measurements and as to the theory of resonance states in multiparticle systems in general. By carrying out a series of computations, we show how (quasi) localization of these resonances takes place. The results confirm the existence of the D-2 resonance just below the energy of the He 2s2p P-3(o) resonance. with which it overlaps. The localization of the two He- resonances is achieved already at the single-configuration level, provided the orbitals are calculated by solving state-specific restricted Hartree-Fock (HF) equations. Accounting for orbital flexibility and relaxation due to the self-consistent interactions is essential to the achievement of a local energy minimum. The localized nature of the wavepacket is revealed even more definitely by solving appropriate multiconfigurational HF (MCHF) equations containing the information from the self-consistent interaction with closed channels as well as with the neighboring significant open ones. Reaching a reliable MCHF solution for a variety of polyelectronic multiply excited states may often be difficult, but once it is achieved it provides the overwhelmingly dominant characteristics of the state. It is then used as the reference wave function for computing variationally the remaining of the localized electron correlation in terms of optimized analytic orbitals representing very nearly the full space of the electron virtual excitations. The calculation of the localized part Psi (0) and of E-0= < Psi (0)/H/Psi (0)>, is done by nonorthonormal configuration interaction (NONCI) since parts of Psi (0) are optimized separately in terms of their own basis sets. The final Psi (0)s for the two resonances consisted of 683 symmetry-adapted configurations for the P-2(o) state and 778 ones for the D-2 state. Using these functions and final state scattering functions with continuum orbitals obtained numerically in term-dependent core potentials, without and with polarization, of a number of lower-lying open channels, we employed the independent channel approximation and computed partial and total energy shifts and widths, the latter from energy-dependent golden rule expressions. Critical comparison of our results for E= E-0 + Delta, where Delta is the shift induced by the interaction of Psi (0) with the continuum, and for the width, Gamma, with the existing few experimental and theoretical values, led us to the conclusion that the E and Gamma lie in the following ranges: For the P-2(o) state: E=57.204 +/-0.005 eV, Gamma =68-74 meV, and for the D-2 state: E=58.295 +/-0.010 eV. Gamma = 38-55 meV. Of special theoretical and experimental interest is the determination of the partial and total widths of the three-electron He- D-2 resonance, since it overlaps from below the two-electron threshold state He 2s2p (3)p(o) whose position is at 58.312 eV with a width of 8 meV.	en
heal.publisher	AMERICAN PHYSICAL SOC	en
heal.journalName	PHYSICAL REVIEW A	en
dc.identifier.isi	ISI:000172074200036	en
dc.identifier.volume	6405	en
dc.identifier.issue	5	en