Explicitly Correlated Electronic Structure Methods for Predictive Energetics and Kinetics of Radical Reactions Edward Valeev Department of Chemistry,Virginia Tech, Blacksburg,VA 24060 Perturbative Explicitly-Correlated Coupled-Cluster Methods
He atom wavefunction 0.055
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We developed a novel perturbative approach, CCSD(2)R12, that incorporates interelectronic distances rij into the highly-accurate coupled-cluster wavefunctions. Unlike conventional counterparts, such explicitly-correlated wavefunctions behave like the exact wavefunction when electrons approach each other closely and, as a consequence, do not suffer from the ubiquitous basis-set problem that plagues accurate quantum-chemical methods. Our CCSD(2)R12 method has much smaller, faster-decreasing basis set errors than the conventional CCSD method, at roughly the same cost! The new method has significant technical advantages over the alternatives. Our approach has also produced an R12 version of the CCSD(T) method, the goldstandard of quantum chemistry.
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Extend our new approach to treat radicals in electronically-excited states and test its performance for several prototypical hydrocarbon chemistries.
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Exact/R12
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Atomization Energy Heat of Formation Mean absolute basis set error, kJ/mol
Future Goals
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Applications to Predictive Thermochemistry of Radical Species Using the new CCSD(T)R12 method in place of the standard CCSD(T) method allows to reduce the basis-set error of the heats of formation of small radicals computed with the standard HEAT model chemistry to the chemical accuracy level (1 kcal/mol) using only a triple-zeta basis set. Standard approach requires a much costlier quadruple-zeta basis for such accuracy.
Standard
R12 Atomization energy R12 Heat of Formation 10 1 kcal/mol
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1 kJ/mol
DZ
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QZ Basis Set
5Z
