			15min:

USING A NON-PRODUCT QUADRATURE GRID TO COMPUTE THE VIBRATIONAL SPECTRUM OF C₂H₄.

GUSTAVO AVILA AND TUCKER CARRINGTON JR., Chemistry Department, Queen's University, Kingston, Ontario K7L 3N6, Canada.

We present an accurate 12-D basis set calculation of the lowest 100 energy levels of the C₂H₄ molecule. A Smolyak non-product quadrature grid, a pruned product basis set, and the Lanczos algorithm are used. This scheme allows one to reduce the size of the basis set by almost 7 orders of magnitude (from 9× 10¹² to 1.3× 10⁶) and the size of the quadrature grid by almost 6 orders of magnitude (from 5.6× 10¹³ to 1.52 × 10⁸). Basis pruning and the nonproduct quadrature grid therefore enable us to solve a problem, numerically exactly, that would be impossible without these tools.