A new natural occupations based spin contamination correction scheme developed and implemented for BS-DFT calculationsRead less
![BS-B3LYP BS-TPSS BS-TPSS:DKH 5Σ+, MCSCF+FOCI SA-BLYP ________________5Σ+, MCSCF+FOCI 7Σ+, MCSCF+FOCI BS-TPSSh _________4X, FeH __7Σ+, MCSCF+FOCI 5X, BMK: Spin-uncorrected MCPF 5X, BMK: Spin-corrected __2X, NiH BS-BMK _______________4X, TiH __ _______7X, BMK __3X, CoH __5X, BMK SA-B3LYP BS-BMK:DKH __________1X, CuH 5X, TPSS: Spin-uncorrected 5X, TPSS: Spin-corrected MCSCF+SOCI __ ____________________7X, TPSS __5X, TPSS Derivation and implementation of the pairwise spin-contamination correction and application to study potential energy curves for 3d transition metal hydrides from BS-DFT σ* SatyenderGoel†‡ and Artëm E. Masunov†‡* 1H1 1H1 σ † Nanoscience Technology Center, ‡ Department of Chemistry, * Department of Physics, University of Central Florida, Orlando, FL – 32826 - + + = S Motivation Spin-Contamination in Unrestricted Density Functional Theory (DFT) Calculations For systems with a multiplicity other than one, it is not possible to use the RHF method as is. Often an unrestricted SCF calculation (UHF/UKS) is performed. The advantage of unrestricted calculations is that they can be performed very efficiently. A disadvantage of UKS approach is that spin-polarized Slater determinant is no longer an eigenfunction of the spin operator. Hence, the average value of <Ŝ2> is not, generally equal to the correct value of Sz(Sz+1). This situation is known as spin contamination and <Ŝ2> is often used as its measure. The common rule is to neglect spin contamination if <Ŝ2> differs from Sz(Sz+1) by less than 10%. As a result of spin contamination, molecular geometry may be distorted toward the high-spin state one, spin density often becomes incorrect, and electron energy differs from the pure spin state ones. Spin-contamination correction based on Natural Occupations (NO) Validation 3. Spin correction based on natural occupation CCSD(T) calculations 2. Spin correction by Eq. : …new approach Basis set used: aug-cc-pVQZ , <Ŝ2> is Sz(Sz+1) where, Sz is ½ of the difference in total numbers of α and β electrons. …by Yamaguchi et. al. DFT functionals ,[object Object]](https://image.slidesharecdn.com/spincorrection-12758428316836-phpapp02/85/Spin-Correction-1-320.jpg)
