Truth and tractability:compromising between accuracy and computational cost in quantum computational chemistry methods for noncovalent interactions and metal-salen catalysis

Quantum chemistry;Ab initio;Noncovalent Interactions;Electronic stucture;Metal-salen;Computational chemistry

Takatani, Tait ; Chemistry and Biochemistry

University:Georgia Institute of Technology

Department:Chemistry and Biochemistry

关键词: Quantum chemistry;    Ab initio;    Noncovalent Interactions;    Electronic stucture;    Metal-salen;    Computational chemistry;   

Others  :  https://smartech.gatech.edu/bitstream/1853/34764/1/takatani_tait_r_201008_phd.pdf

美国|英语

来源: SMARTech Repository

【 摘 要 】

Computational chemists are concerned about two aspects when choosing between the myriad of theoretical methodologies: the accuracy (the"truth") and the computational cost (the tractability).Among the least expensive methods are the Hartree-Fock (HF), density functional theory (DFT), and second-order Moller-Plesset perturbation theory (MP2) methods.While each of these methods yield excellent results in manycases, the inadequate inclusion of certain types of electron correlation (either high-orders or nondynamical) can produce erroneous results.The compromise for the computation of noncovalent interactions often comes from empirically scaling DFT and/or MP2 methods to fit benchmarkdata sets.The DFT method with an empirically fit dispersion term (DFT-D) often yields semi-quantitative results.The spin-componentscaled MP2 (SCS-MP2) method parameterizes the same- and opposite-spin correlation energies and often yields less than 20% error for prototypenoncovalent systems compared to chemically accurate CCSD(T) results.There is no simple fix for cases with a large degree of nondynamicalcorrelation (such as transition metal-salen complexes).While testing standard and new DFT functionals on the spin-state energy gaps oftransition metal-salen complexes, no DFT method produced reliable results compared to very robust CASPT3 results.Therefore each metal-salencomplex must be evaluated on a case-by-case basis to determine which methods are the most reliable.Utilizing a combination of DFT-D and SCS-MP2 methods, the reaction mechanism for the addition of cyanide to unsaturated imides catalyzed by the Al(Cl)-salen complex was performed.Various experimental observations are rationalized through this mechanism.