J. Phys. Chem. 1993,97, 5852-5859
5852
Relativistic and Correlation Effects for Element 105 (Hahnium, Ha). A Comparative Study of M and MO (M = Nb, Ta, Ha) Using Energy-Adjusted ab Initio Pseudopotentials Michael Dolg,'*+Hermann Stoll, and Heinzwemer Preuss Institut f i r Theoretische Chemie, Universitiit Stuttgart, Pfaffenwaldring 55, W-7000 Stuttgart 80, Federal Republic of Germany Russell M. Pitzer Department of Chemistry, The Ohio State University, 120 West 18th Ave., Columbus, Ohio 43210 Received: November I O , I992
Nonrelativistic and quasirelativistic energy-adjusted ab initio pseudopotentials are presented for element 105 (hahnium, Ha) together with corresponding energy-optimizedvalence basis sets. The method of energy adjustment of pseudopotentials is extended to a two-component formalism and to multiconfiguration wave functions. The accuracy of the pseudopotential scheme is demonstrated by a comparison of atomic valence-only results to corresponding all-electron data. Atomic multiconfiguration self-consistent field and multireference configuration interaction calculations for M and M+ (M = Nb, Ta, Ha) are compared with available experimental data. Corresponding molecular calculations, which included spin-orbit coupling, have been performed for the lowlying states of H a 0 and are compared to the results from corresponding calculations of the lighter homologs NbO and TaO.
1. Introduction Recently the chemistry of superheavy elements like hahnium and (Ha), element 105, has been studied the~retically.~" It is observed experimentally that the HaV complexes with fluorineand chlorine more closely resemble those of the lighter homolog NbVinstead of the heavier homolog TaV, e.g., complexes of the type MOC14-and MOC1S2-(M = Nb, Ha) are formed in weak and strong hydrochloric acid solution, respectively, in contrast to TaCl6- and TaC172-. Due to the very short half-life of the most stable Ha isotope (262Ha,q p = 34 s) experimental work in Ha chemistry is rather difficult and quantum chemical calculations on Ha compounds should be helpful in understandingthe experimentallyobserved phenomena. Atomic multiconfigurationDiraoFock results for the first five ionization potentials of Ha are available6and comparative relativisticDiracSlater discrete-variational studies of the pentahalides MXSand oxytrihalides MOX3 (M = C1, Br) of group 5 elements M have recently been publi~hed.~-~ Quasirelativistic energy-adjusted pseudopotentials and corresponding energy-optimized valence basis sets have been derived for almost all elements of the periodic table7-I4and provide a convienient and efficient tool for the quantum chemical investigation of heavy element compounds. The high accuracy of this pseudopotential method (which is completely based on quantum mechanical observables in contrast to other methods15J6based on one-particle properties) has been demonstrated recently for Hg, HgH, and their cations by a comparison of valence-only results to those of correspondingatomic and molecular all-electron calculation^.^^ In this contribution we present nonrelativistic(onecomponent) and quasirelativistic (one- and two-component, i.e., with and without averaging over spin-orbit effects) energyadjusted pseudopotentials for Ha together with energy-optimized valence basis sets. A thorough comparison of atomic pseudopotential results with corresponding all-electron data is used to judge the accuracy of the applied pseudopotential method. Special attention is paid to the choice of the all-electron method used to derive the reference data for quasirelativistic pseudopotentials; Le., the accuracy of
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thequasirelativisticextension of the Hartree-Fock (HF) method,18 the so-called Cowan-Griffin (CG)I9 or Wood-Boring (WB)20 scheme, previously used in the generation of pseudopotentials for heavy main groupelements,I2transition elements,8lanthanoids,9J0 and actinoids," is compared to the presumably more accurate Dirac-Fock scheme.21 In addition, the question as to whether accurate one-component,i.e., spin-orbit averaged, quasirelativistic pseudopotentiafs can be derived by averaging two-component quasirelativistic pseudopotentials is addressed. The results of atomicpseudopotentialself-consistent field (SCF) calculations, multiconfiguration self-consistent field (MCSCF) calculations carried out within the complete active space (CASSCF) formalism, and multireference configuration interaction (MRCI) calculations corrected for size consistency errors with the Langhoff-Davidson formulazzas well as averaged coupledpair functional (ACPF) calculationsfor Nb, Ta, and their cations are compared to available experimental data.23 The results are used to estimate the accuracy of corresponding predictive calculationson Ha and Ha+. As a first molecular application of the Ha pseudopotentials and valence basis sets we predict the spectroscopicconstantsfor the2Aground state and the 42-excited state of H a 0 and compare them to the corresponding values for the TaO 2A and NbO 42-ground states. The role of differential relativistic and correlation effects for atomic excitation and ionization energies as well as for molecular constants of H a 0 is discussed. Work on various halogen and oxy-halogen complexes of the group 5 (Vb) elements V, Nb, Ta, and Ha is currently unterway in our laboratory and will be published elsewhere. 2. Methods
The method of energy adjustment of nonrelativistic and quasirelativistic ab initio pseudopotentialshas been outlined in a number of papers (cf. ref 12 for a recent account) and will only be briefly discussed here. The valence model Hamiltonian (in atomic units) used in this work is 1 1 QAQ, %, = - - x A i Vpp - i- 2 i i
