Broken-Symmetry Unrestricted Hybrid Density Functional Calculations on Nickel Dimer and Nickel Hydride

Authors

Cristian V. Diaconu
Art E. Cho
J. D. Doll
David L. Freeman, University of Rhode IslandFollow

Document Type

Article

Date of Original Version

11-22-2004

Department

Chemistry

Abstract

In the present work we investigate the adequacy of broken-symmetry unrestricted density functional theory for constructing the potential energy curve of nickel dimer and nickel hydride, as a model for larger bare and hydrogenated nickel cluster calculations. We use three hybrid functionals: the popular B3LYP, Becke’s newest optimized functional Becke98, and the simple FSLYP functional (50% Hartree – Fock and 50% Slater exchange and LYP gradient-corrected correlation functional) with two basis sets: all-electron (AE) Wachters+ f basis set and Stuttgart RSC effective core potential (ECP) and basis set. We find that, overall, the best agreement with experiment, comparable to that of the high-level CASPT2, is obtained with B3LYP/AE, closely followed by Becke98/AE and Becke98/ECP. FSLYP/AE and B3LYP/ECP give slightly worse agreement with experiment, and FSLYP/ECP is the only method among the ones we studied that gives an unacceptably large error, underestimating the dissociation energy of Ni₂ by 28%, and being in the largest disagreement with the experiment and the other theoretical predictions. We also find that for Ni₂, the spin projection for the broken-symmetry unrestricted singlet states changes the ordering of the states, but the splittings are less than 10 meV. All our calculations predict a δδ-hole ground state for Ni₂ and δ-hole ground state for NiH. Upon spin projection of the singlet state of Ni₂ , almost all of our calculations: Becke98 and FSLYP both AE and ECP and B3LYP/AE predict 1 ( d ^A _x2_-y2d ^B _x2-_y2 d ^B ) or ¹ ( d ^A _xy d ^B_xy) ground state, which is a mixture of ¹ Σ_g⁺ and 1Γ_g. B3LYP/ECP predicts a ³(d ^A_x ² _{- y} ² d^B_xy )(mixture of ³Σ _g ^- and ³Γ_u ) ground state virtually degenerate with the ¹ (d ^A_x2 - _y 2 d^B_x 2 - _y 2 )/ ¹ (d^A_xy d^B_xy ) state. The doublet δ-hole ground state of NiH predicted by all our calculations is in agreement with the experimentally predicted ² ^ ground state. For Ni₂ , all our results are consistent with the experimentally predicted 0_g⁺ (a mixture of ^l Σ_g⁺and ³Σ _g^-) or 0_u^-(a mixture of ^l Σ^_u-and Σu ⁺).

Citation/Publisher Attribution

Diaconu, C. V., Choi, A. E., Doll, J. D., & Freeman, D. L. (2004). Broken-Symmetry Unrestricted Hybrid Density Functional Calculations on Nickel Dimer and Nickel Hydride. Journal of Chemical Physics, 121(20), 10026-10040. doi: 10.1063/1.1798992

Available at: http://dx.doi.org/10.1063/1.1798992

Publisher Statement

© 2004 American Institute of Physics.