Ab initio studies of the water dimer using large basis sets: The structure and thermodynamic energies

Articles you may be interested in Ab initio molecular dynamics study of water at constant pressure using converged basis sets and empirical dispersion corrections Interaction optimized basis sets for correlated ab initio calculations on the water dimer Ab initio calculation of the interaction potential for the krypton dimer: The use of bond function basis sets Efficient elimination of basis set superposition errors by the local correlation method: Accurate ab initio studies of the water dimer Convergence to the basis‐set limit in ab initio calculations at the correlated level on the water dimer Ab initio calculations with various large basis sets have been performed on the water dimer in order to study the structure, energetics, spectra, and electrical properties. As a reference system, the calculations of the water monomer were also performed. The second order M0ller-Plesset perturbation theory (MP2) using a large basis set (O:13s,8p,4d,2j/H:8s,4p,2d) well reproduces various water monomer experimental data except for the somewhat underestimated absolute energy and hyperpolarizability. The monomer energy calculated with the fourth-order M0ller-Plesset perturbation theory (MP4) with the above basis set is-76.407 hartrees, which is only 0.073 hartree above the experimental energy. To compare the theoretical and experimental dimer structures and thermal energies accurately, we summarized the quantum statistical thermodynamic quantities with corrections for anharmonic vibration, rotation, rotation-vibration coupling, and internal rotation. With the correction for the anharmonic binding potential and rotation, the predicted interoxygen distance of the dimer is 2.958 A, which is so far the closest to the experimental value-2.976 A. The predicted dimer dipole moment is 2.612 D, which is the first agreement with experiment (2.60-2.64 D). The predicted frequency shift of the dimer with respect to the monomer is in good agreement with experiment. With the MP2 calculation using the large basis set, the basis set superposition error correction (BSSEC) of the dimer is only 0.33 kcal/mol, which is by far the smallest among the MP2 results reported. Without BSSEC, the predicted binding energy, enthalpy, free energy, and entropy are all in good agreement with experiment within the error bounds, whereas with BSSEC, some of them seem to be slightly off the experimental error bounds. Nevertheless, the results with BSSEC can be more reliable than those without BSSEC.