Electronic states of CuO

摘要

AbinitioSCF and CI calculations are reported for the ground state and lowhyphen;lying excited electronic states of CuO (i.e., within sim;20times;103cmminus;1of theXtilde;thinsp;2Pgr; ground state), employing anabinitioeffective potential for the Cu atomic core (1sndash;3p), and including comparisons of several atomic orbital basis sets. The calculated bond lengths, energy separation, and population analyses for the lowest two electronic states,Xtilde;thinsp;2Pgr; andYthinsp;2Sgr;+lsqb;corresponding roughly to Cu+(3d10) and Ominus;(2p5), where the 2poxygen hole is, repectively, 2ppgr; and 2psgr;rsqb;, do not vary appreciably among the basis sets tested (minimal and split valence bases on Cu, and a split valence basis on oxygen, with and withoutdhyphen;polarization functions and diffusepfunctions on oxygen) and are in reasonable agreement with previous experimental and theoretical estimates. Most of the remaining excited states of CuO below sim;20times;103cmminus;1may be rationalized in terms of atomichyphen;like excitations originating from theXtilde;thinsp;2Pgr; ground state: 3d(Cu)thinsp;rarr;thinsp;4s(Cu) and 3d(Cu)thinsp;rarr;thinsp;2thinsp;ppgr;(O) (the latter formally corresponds to Cu2+O2minus;, though covalent 2plsquo;gsndash;4sbonding reduces the charge to sim;Cu+Ominus;). Close agreement (rms deviation of sim;103cmminus;1) is obtained between calculated (CI) and observed adiabatic transition energies for ten Sgr;, Pgr;, and Dgr; doublet excited states (relative to theXtilde;thinsp;2Pgr; state), after the calculated excitation energies are reduced by sim;5times;103cmminus;1, a term which corrects primarily for limitations in the Cu atom basis set, and whose magnitude can be obtained both in terms of calculated and observed atomic quantities and by direct leasthyphen;squares fitting of calculated and observed CuO transition energies. The calculations yield the first comprehensive assignment of Kronig symmetry (plusmn;) for the observed2Sgr; states (dgr;thinsp;2Sgr;minus;,Athinsp;2Sgr;minus;,Aprime;thinsp;2Sgr;+, andGthinsp;2Sgr;+) and one which is consistent with recent analyses of experimental data. The extent of specific molecular correlation effects is analyzed, and found to be important in the assignment of several of the observed transitions. The CI mixing of different principal configurations may be significant for states involving the lsquo;lsquo;Cu2+O2minus;rsquo;rsquo; configuration (as also suggested in previous studies), and the assignments based on the present CI results for these states are only tentative.