Towards the intrinsic error of the correlation consistent Composite Approach (ccCA)

Highly energetic nitrogen species: Reliable energetics via the correlation consistent Composite Approach (ccCA)

“…The zero-point vibrational energies and enthalpy corrections were scaled by a factor of 0.9890 [26], to account for deficiencies in the harmonic approximation. Singlepoint calculations were carried out at the B3LYP/cc-pVTZ optimized geometries for each of the ccCA steps [26], which include a series of MP2/aug-cc-pVnZ (where n = D,T,Q) calculations for which the SCF and MP2 energies were then extrapolated to the CBS limit. A two point exponential extrapolation scheme developed by Feller and co-workers [48,49] was used for the SCF extrapolation:…”

“…Our group has developed an ab initio composite method free from empirical parameters called the correlation consistent Composite Approach (ccCA) [23][24][25][26]. The method has been successful in the prediction of energetic properties, even where other composite approaches have had difficulties (e.g., s-block [27]) or may be undeveloped or in their infancy (e.g., for transition metal species [25,28]).…”

A simple way to predict vibrational zero point energy of organophosphorus (III) compounds

“…To remedy this problem, the calculation of these quantities through current techniques of computational quantum chemistry or with empirical rules is needed. Currently, a number of options exist for the accurate determination of thermochemical data (generally defined as ±1 kcal/-mol) for small and medium-sized molecules, such as the theory Gn [8], CBS-QB3 [9,10] and the ccCA approach [11,12]. When these approaches are extended to large systems, it is becoming increasingly clear that the limiting factor for the thermochemical accuracy could be the nuclear movement rather than the electronic structure [13,14].…”

The importance of secondary structure in determining CO2-protein binding patterns

“…3. To estimate the strength of a typical CO 2 -backbone hydrogen bond, the binding energy of CO 2 to N-methylacetamide (which has previously been suggested as an appropriate backbone model) [43] was calculated using the highly accurate correlation-consistent composite approach (ccCA) [23, 44,45], which yields a CO 2 -backbone hydrogen-bond strength of 1.5 kcal mol −1 , in line with the strength of an intrapeptide hydrogen bond (1-2 kcal/mol) [2]. The side-on, purely electrostatic interaction is weaker still, but it can nevertheless influence CO 2 affinity among the two secondary structure types.…”