On the performance of energy-consistent spin±orbit pseudopotentials: 111)H revisited Michael Dolg a, * , Hermann Stoll b , Michael Seth c , Peter Schwerdtfeger d a Institut fur Physikalische und Theoretische Chemie, Universitat Bonn, Wegelerstr. 12, D-53115 Bonn, Germany b Institut fur Theoretische Chemie, Universitat Stuttgart, D-70550 Stuttgart, Germany c Department of Chemistry, University of Calgary, Calgary, Canada T2N 1N4 d Department of Chemistry, The University of Auckland, Private Bag 92019, Auckland, New Zealand Received 28 May 2001; in ®nal form 2 August 2001 Abstract A new two-component relativistic pseudopotential PP) of the energy-consistent EC) variety, adjusted to multi- con®guration Dirac±Hartree±Fock MCDHF) data, is presented for the superheavy element 111 and is applied in correlated valence ab initio calculations, with and without inclusion of spin±orbit SO) coupling, to the determination of spectroscopic constants of the element 111 monohydride. Good agreement with a recent study by Han and Hirao [Chem. Phys. Lett. 328 2000) 453] is found, and it is concluded that a direct two-component PP ®t is superior to a previously practiced two-step scalar-relativistic/SO) adjustment procedure. We estimate the molecular constants of element 111 monohydride to be R e  1:529  A, D e  2:83 eV and x e  2642 cm 1 . Ó 2001 Elsevier Science B.V. All rights reserved. 1. Introduction It is commonly accepted nowadays that pseud- opotentials PPs) provide a both economic and reliable means of incorporating scalar-relativistic eects into quantum-chemical ab initio calcu- lations for heavy-element compounds [1]. The situation is less clear-cut for the concomitant spin±orbit SO) potentials, for at least three rea- sons. First, it is not fully clear theoretically, how well a transformation from the all-electron AE) case, with its heavy sampling of the near-nuclear region, to the PP case, with SO potentials mainly acting in the outer-core/valence region, can work. Secondly, reliable two-component PP, AE) or four-component AE) benchmark calculations including SO eects, at the basis-set limit and with a good account of electron correlation, are still extremely rare, even for diatomics with a single heavy atom. Thirdly, the extraction/comparison of PP or AE SO eects necessitates the de®nition of a scalar-relativistic `reference point' which is meth- od-dependent and non-unique. In a recent Letter [2], Han and Hirao compared the performance of shape-consistent SC, [3]) as well as energy-consistent EC, [4]) PPs for the superheavy element 111 Eka-Au), in one- and two-component Hartree±Fock HF) and coupled- cluster with singles, doubles and perturbative triples, CCSDT)) calculations for molecular con- stants R e , x e , D e ) of the monohydride 111)H. While they found very similar results at the scalar- 21 September 2001 Chemical Physics Letters 345 2001) 490±496 www.elsevier.com/locate/cplett * Corresponding author. Fax: +49-228-73-9066. E-mail address: dolg@thch.uni-bonn.de M. Dolg). 0009-2614/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved. PII: S 0 0 0 9 - 2 6 1 4  0 1 ) 0 0 9 0 1 - 0