Do composite methods achieve their target accuracy?

Abstract

Enthalpies of formation have been calculated for the 147 molecules of the G2/97 data set using the correlation consistent Composite Approach (ccCA) to assess the ability of this approach to achieve its presumed CCSD(T)-level accuracy. The calculated enthalpies of formation from the G2/97 data set were compared to enthalpies computed at the CCSD(T,FC1)/aug-cc-pCV∞Z-DK level of theory. Deviations of both ccCA and CCSD(T) enthalpies from experiment have been evaluated. ccCA results in a mean absolute deviation (MAD) of 0.80 kcal mol-1 from experiment while CCSD(T) has an MAD of 0.90 kcal mol-1. The MAD of the ccCA enthalpies from the CCSD(T,FC1)/aug-cc-pCV∞Z-DK enthalpies is 0.87 kcal mol-1 .

Domain‐based local pair natural orbital methods within the correlation consistent composite approach

“…Numerous approaches have been developed over the years to try to reduce the computational cost associated with high‐level ab initio methods while maintaining similar accuracy. These approaches include but are not limited to ab initio composite methods, which use a series of less computationally expensive and accurate methods to estimate electronic energies calculated through high‐level methodologies, and local ab initio correlated methods, which reduce CPU time by localizing and screening molecular orbitals (MOs) to decrease computational cost. The combination of these approaches should, in principle, expand the range of molecules that can be targeted with composite methodologies since composite methods are not as efficient for larger molecules but achieve a high‐level of accuracy for well‐established reliable experiments and local methods reduce the CPU time while reproducing electronic energies analogous to canonical MO methods.…”

A big data framework to validate thermodynamic data for chemical species

“…The estimation of enthalpies of formation using high level electronic structure calculations is computationally demanding. To compound the problem, care must be taken to choose the right level of theory [15,16,17], the errors in the method scale with the size of the species [18,19], and various correction terms are needed to achieve accurate estimates [20]. The calculations become intractable for large molecules [17,21] and such methods are not suitable for large scale analysis.…”

A systematic method to estimate and validate enthalpies of formation using error-cancelling balanced reactions

“…The standard enthalpies of formation for various titanium-containing species considered in this work were also calculated by Wang et al [84] using the computationally demanding coupled-cluster method with complete basis set extrapolation (CCSD(T)/CBS). This is currently considered the "gold standard" of quantum chemistry [40]. a Calculated using isodesmic reactions using the reference values dened in Table 1 and the set of species containing carbon, hydrogen and oxygen [67].…”

“…This type of single-point calculation is computationally demanding. The errors scale with the size of the molecule [40,41], and the calculations become intractable for large molecules [42,43]. In addition, care must be taken to choose the right level of theory [44,45,42] and various correction terms needed to achieve consistent and accurate estimates.…”