Efficient quantum calculation of the vibrational states of acetylene

We present full-dimensional quantum mechanical calculations of the vibrational states of acetylene. The calculation scheme is a combination of several methods. The molecular Hamiltonian is represented in CH-CH diatom-diatom Jacobi coordinates. Phase space optimized discrete variable representation is used to construct effective one-dimensional basis functions for radial coordinates, and a basis contraction strategy is applied to angular coordinates. Parity and diatom-diatom permutation symmetry are exploited. The final Hamiltonian matrix is sparse, and an iterative technique combined with an efficient preconditioner is employed to calculate the eigenvalues within desired spectral windows. It is shown that our computation is efficient and accurate, and nearly ideal scaling with respect to increasing energy is achieved. (C) 2012 Elsevier B.V. All rights reserved.