The argon-water van der Waals complex is characterized by the potential energy surface of a hindered free rotor with two shallow minima, the minima corresponding roughly to hydrogen-bonded and dipole-induced-dipole bound structures.  The three-dimensional surface for the van der Waals interaction was calculated (with relaxed water geometry) at 4940 points at the CCSD(T)/aug-cc-pVTZ level.  This surface was then interpolated to a fine grid using a Kriging interpolation for solution of the vibrational Schrödinger equation by the finite element method using the package <i>FEMvib</i>.  The finite element method employed a 30×30×30 grid of 27-noded hexahedra and quadratic Lagrange shape functions to estimate the solutions, subject to periodic boundary conditions along the angular coordinates.  The dynamic G-matrix elements that generate the kinetic energy operator are calculated directly from the set of partially-optimized geometries used to create the PES.  Energy levels of the J=0 states were thereby predicted to mean errors within 10% of experimentally observed values for the first 15 vibrational states, encompassing excitation along all three modes.  Although resource-intensive, these grid-based methods allow the solution of highly coupled, highly anharmonic vibrational problems of low dimensionality with close to black-box simplicity.

Fully <i>ab initio</i>, vibrational analysis of Ar-H2O van der Waals complex by the finite element method

251st National Meeting (2016)

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Fully ab initio, vibrational analysis of Ar-H2O van der Waals complex by the finite element method