Quantum Chemistry Composite Methods - Weizmann-n Theories

Weizmann-n Theories

The Weizmann-n ab initio methods (Wn, n = 1–4) are highly-accurate composite theories devoid of empirical parameters. These theories are capable of sub-kJ/mol accuracies in prediction of fundamental thermochemical quantities such as heats of formation and atomization energies, and unprecedented accuracies in prediction of spectroscopic constants. The ability of these theories to successfully reproduce the CCSD(T)/CBS (W1 and W2), CCSDT(Q)/CBS (W3), and CCSDTQ5/CBS (W4) energies relies on judicious combination of very large Gaussian basis sets with basis-set extrapolation techniques. Thus, the high accuracy of Wn theories comes with the price of a significant computational cost. In practice, for systems consisting of more than ~9 non-hydrogen atoms (with C1 symmetry), even the computationally more economical W1 theory becomes prohibitively expensive with current mainstream server hardware.

In an attempt to extend the applicability of the W1 and W2 ab initio thermochemistry methods, explicitly correlated versions of these theories have been developed (W1–F12 and W2–F12). W1–F12 was successfully applied to to large aromatic systems (e.g., tetracene) as well as to systems of biological relevance (e.g., DNA bases).