TOPOND : A PROGRAM FOR THE APPLICATION OF THE QUANTUM THEORY OF ATOMS IN MOLECULES TO PERIODIC SYSTEMS. Carlo Gatti, CNR Centro per lo Studio delle Relazioni fra Struttura e Reattività Chimica, via Golgi 19, 20133 Milano, ITALY

The TOPOND program implements the Quantum Theory of Atoms in Molecules¹ (QTAM) to periodic systems in N (N=0-3) dimensions. The program is interfaced to CRYSTAL-92² (and CRYSTAL-95 pre-release) package. A preliminary version of TOPOND has been described elsewhere³, together with its first application to the urea³ and ice VIII⁴ molecular crystals. TOPOND is presently divided in five sections. The first two implement the topological analysis of the electron density ([[rho]]) and of its Laplacian ((²[[rho]]) scalar fields. An option for an automated search of critical points (Cps) is provided and two different search algorithms can be exploited (Newton Raphson or eigenvector following techniques). Analytic representations of the atomic interaction lines may be evaluated and the associated bond path lengths determined. The fourth section of TOPOND computes atomic properties which may be obtained either following an indirect³ determination of the zero-flux surfaces or using a combination of the indirect with the standard⁵ direct methods. The last section performs the grid evaluation of [[rho]], (²[[rho]], |([[rho]] | functions and traces out molecular graphs, or generically, ([[rho]] trajectories in selected crystalline planes. The electron localization function (ELF), along with other local and integral properties (kinetic energy densities) which depend on the non-diagonal elements of the first order density matrix, can now also be computed.

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