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Abstract
Accurately predicting bond length and bond dissociation energy for bimetallic diatomic molecules that involve metalmetal multiple bonds is a great challenge for electronic structure theory, in part because many of these molecules have inherently multiconfiguration wave functions, a characteristic that is variously labeled as strong correlation or multireference character. Although various popular density functionals are widely used in studying metalmetal bonding in catalysis, their accuracy can be questioned, and it is important to see both how well and how poorly a functional can perform. Here we test 50 KohnSham exchangecorrelation density functionals for selected 3d and 4d hetero and homonuclear bimetallic diatomic molecules against experimental bond lengths and bond energies. We found that for the majority of the density functionals, the mean unsigned error in predicting the bond length is larger than 0.08 Å, and for the bond energy, half of the functionals give a mean unsigned error larger than 20 kcal mol^{1}. This indicates that such highly multireference bimetallic systems are challenging for KSDFT. However, some exchangecorrelation functionals perform significantly better than average for both bond energies and bond lengths, in particular, BLYP, M06L, N12SX, OreLYP, RPBE, and revPBE, and are recommended for both kinds of calculations. Other functionals that perform relatively well for bond lengths include MGGAMS0, MOHLYP, OLYP, PBE, and SOGGA11, and other functionals that perform relatively well for bond energies include GAM, M05, M06, MN15, and τHCTHhyb. Although some of these functionals (M05, M06, MN15, N12SX, and τHCTHhyb) contain a nonzero percentage of HartreeFock exchange, a broader conclusion is that HartreeFock exchange brings in a static correlation error and usually tends to make the results, especially the bond lengths, less accurate. We find some significant differences between allelectron calculations and calculations with effective core potentials. For analysis, the article also presents CASSCF calculations of the percentage contributions of the dominant configurations, and the paper compares orbitals and configurations obtained in DFT calculations to those in CASSCF calculations. The equilibrium bond distance of Rh_{2} is not available from experiments, and we predict it to be 2.22 Å. The bond energy of VCr is not available from experiments, and we predict it to be 52.9 kcal mol^{1}.
Original language  English (US) 

Pages (fromto)  58395854 
Number of pages  16 
Journal  Physical Chemistry Chemical Physics 
Volume  19 
Issue number  8 
DOIs  
State  Published  2017 
Bibliographical note
Publisher Copyright:© 2017 the Owner Societies.
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 1 Finished

Energy Frontier Research Center For Inorganometallic Catalyst Design (DESC0012702)
Gagliardi, L. (PI), Cramer, C. (CoI), Lu, C. C. (CoI), Penn, L. (CoI), Stein, A. (CoI) & Truhlar, D. G. (CoI)
U.S. DEPARTMENT OF ENERGY (USDOE)
8/1/14 → 7/31/18
Project: Research project