Explicitly Correlated Electronic Structure Methods for Predictive Energetics and Kinetics of Radical Reactions Edward Valeev Department of Chemistry,Virginia Tech, Blacksburg,VA 24060 High-Rank Explicitly-Correlated Coupled-Cluster Methods
Using the novel CCSDTQ-R12 method were were able to solve the electronic Schrodinger equation for water molecule with an 0.004 % accuracy (2 kcal/ mol) without any empirical corrections. The extra cost of the R12 terms in the practical formulations of such methods, such as our CCSD(T)R12, are almost negligible.
He atom wavefunction 0.055
0.05 q
0.045 ^
We developed novel accurate electronic structure methods that incorporate interelectronic distances rij without undue extra cost. 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.
0.04
0.035
Standard
0.03 -100
-50
vs
Exact/R12
0 q
50
100
dissociation of N2 molecule
Universal Explicitly-Correlated Methods
ï0.16
Future Goals Benchmark the performance of the efficient CC-R12 methods for computing reaction barriers and extend the universal R12 method to treat excited states.
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Etotal ï ECASSCF [Hartree]
We developed a universal R12 method that can be used to improve any wave function, single- or multi-reference. In an initial application to the dissociation of the triple bond in N2 only a double-zeta basis was required with the R12 method to match the accuracy of the standard quadruple-zeta result.
ï0.2
aDZ MRCI[2]R12 ~ aQZ MRCI
ï0.22 ï0.24 ï0.26 aDZ aTZ aQZ aTQZ aDZ [2]R12
ï0.28 ï0.3 0.5
1
1.5
2 2.5 3 3.5 NïN distance [Ångström]
4
4.5
5
