Complete Basis Set Limit Interaction Research Articles

Understanding the interactions between hydrogen-bonded complexes of xylose and water: Quantum Chemical Investigation

Hydrogen-bonded complexes between xylose and water, modelled by xylofuranose…H2O complexes were explored employing ab initio quantum chemical framework. The Moller–Plesset second-order perturbation theory (MP2) in conjugation with aug-cc-pVDZ basis set, is used for investigating the H-bonding interactions. The complete basis set limit interaction energies for α-and β-xylofuranose and xylopyranose water complexes were calculated at MP2 level. It is observed that the addition of water molecule does not change the conformational structure of xylose moieties. Further water is found to interact with xylose mainly through the O atom present in a ring and its neighboring OH group. Energy decomposition analysis by LMO-EDA approach indicates that the electrostatic and exchange interactions are the two largest contributing terms to the total interaction energy for bonding between Xylose and water. The nature of interaction between xylose and water is investigated by means of MP2/CBS interaction energies, energy decomposition analysis, change in vibrational frequencies and electron density critical points. It was found that xylofuranose has more affinity towards water than xylopyranose form.

Benchmark Study of the Interaction Energy for an (H2O)16 Cluster: Quantum Monte Carlo and Complete Basis Set Limit MP2 Results

The quantum Monte Carlo method is used to calculate the binding energy of an (H2O)16 cluster that has been the subject of several recent theoretical studies. The resulting interaction energy, -165.1(8) kcal/mol, is very close to our MP2 complete basis set limit interaction energy of -164.1 kcal/mol. Comparison of these results with those for the one-, two-, three-, and four-body interaction energies leads us to conclude that the five- and higher-body interactions are attractive, contributing over 2 kcal/mol to the net interaction energy of this (H2O)16 isomer.

Potential Energy Surface of the Cytosine Dimer: MP2 Complete Basis Set Limit Interaction Energies, CCSD(T) Correction Term, and Comparison with the AMBER Force Field

The complete basis set (CBS) limit of the MP2 interaction energy and the CCSD(T) correction term determined as the difference between the CCSD(T) and MP2 interaction energies were evaluated for 17 stacked and 4 H-bonded structures of the cytosine dimer. Extrapolation to the MP2 CBS limit was done using the aug-cc-pVDZ and aug-cc-pVTZ results, and the CCSD(T) correction term was determined with the 6-31G*(0.25) basis set. Extrapolation to the CBS limit is essential in all parts of the potential energy surface and affects mainly the absolute MP2 stabilization energy. The effect on the relative stability is smaller but not negligible. The CCSD(T) correction term is for stacked structures with large overlaps of the monomers substantially repulsive but not uniform. Thus, when comparing the final estimate (abbreviated as CBS(T)) with previously used medium-level MP2/6-31G*(0.25) data, the CCSD(T) correction partially compensates for the enhanced absolute MP2 CBS stabilization but further increases the relative ...