CESD99 - A new version to represent atomic wave functions in a determinantbasis

Determinant expansions of atomic wave functions have several advantages for calculating transition probabilities and cross sections. For instance, suc h a representation can easily be applied to rather a large number of transi tion operators and also in order to include rearrangement effects of the bo und-state density following the excitation or the decay of an atomic state. In practice, the rearrangement of thr electron density is most simply take n into account if the variation of the initial and final state wave functio ns is carried out separately in studying transition or ionization processes . Of course, such a computational procedure yields sets of one-electron orb itals which are not quite orthogonal to each other and which do require spe cial care in evaluating the (many-electron) transition matrix. For relativistic wave functions of the atomic structure package GRASP92 [F. A. Parpia, C.E Fischer, I.P. Grant, CPC 92 (1996) 249], a determinant repre sentation of the atomic states is obtained by the CESD97 program [S. Fritzs che, I.P. Grant, CPC 103 (1997) 277]. This program performs a complete expa nsion of symmetry-adapted functions and has been found useful in a number o f applications. For accurate transition probability studies, however, often large wave function expansions of several ten or even hundred thousand det erminants are required which cannot be handled by CESD97 due to the demand on memory and computing time. Further difficulties were caused by the tight binding of both GRASP92 and CESD97 to the IBM XL Fortran standard. To over come these difficulties and to facilitate the transfer to other architectur es, CESD97 has entirely been rewritten according to the ANSI standard Fortr an 90/95. The new version, CESD99, considerably improves the efficiency of large computations and, now, enables wave function expansions based on seve ral (hundred) thousand determinants. The conversion to Fortran 90/95 is con sidered as major step to render the CESD program ready to use for systemati c investigations of open-shell atoms. CESD99 is part of the RATIP package f or the calculation of relativistic atomic transition and ionization propert ies and will be distributed within this framework [S. Fritzsche, C.E Fische r, C.Z. Dong, this volume]. (C) 2000 Elsevier Science B.V. All rights reser ved.