Quantum simulations and ab initio electronic structure studies of (H ₂O)^2-

The energetics of the negatively charged water aimer (H₂O) ₂^-, is studied using quantum-simulation techniques and ab initio electronic structure calculations. Using the RWK2-M potentials for water and a pseudopotential for the interaction of an electron with a water molecule in the ground state, consisting of Coulomb, adiabatic polarization, exclusion, and exchange contributions, it was found via the quantum path-integral molecular dynamics and the coupled quantum-classical time-dependent self-consistent field methods that while the minimum energy of (H₂O)₂ ^- corresponds to a nuclear configuration similar to that found for the neutral (H₂O)₂ cluster, other nuclear configurations are also exhibited at finite temperature, characterized by a higher total molecular cluster dipole moment and a larger magnitude of the excess electron binding energy. Quantitative agreement is found between the results obtained by the quantum simulations, employing the excess electron-molecule pseudopotential, and those derived, for selected nuclear configurations, via ab initio calculations, employing the Gaussian 86 code with the basis set for the water molecules supplemented by a large diffuse set located at the midpoint of the two oxygens and in addition by a diffuse set for the excess electron.