Anyone who wants to harvest in his lifetime cannot afford
to wait for the ab initio theory of weather!
Hans Georg von Schnering

Welcome to aixCCAD, the Aix-la-Chapelle Crystal-Chemical Atomic Dynamics computer program from the Institute of Inorganic Chemistry at Aachen University of Technology (RWTH). So, what is the philosophy behind the aixCCAD computer program?

Atomistic simulations such as those of molecular dynamics (MD) type nowadays are well-established scientific tools used in investigating a number of (mostly liquid) chemical systems. Here, the atomic trajectories are found by solving Newton's equations of motion while the interatomic or intermolecular potentials are either based on classical parameterizations or on quantum-mechanical methods ("parameter-free" MD).

Interestingly, solid-state chemistry belongs to those chemical fields in which MD simulations have not been widely used; there are at least two reasons. First, solid-state chemistry has historically concentrated on the synthesis, crystallographic and physical characterization of new compounds; questions concerning chemical reactivity and dynamical phenomena had to stand back. Second, the attempt to use a standard MD-like simulation in modeling a typical solid-state material is ultimately challenged by the fact that most compounds under study are not restricted to a few atom types (such as C, H, N, O) but they mostly are composed of atoms from any part of the periodic table; in other words, any atomistic simulational method for solid-state chemistry immediately faces an incredibly complex parameterization problem.

aixCCAD has been designed keeping the problems of solid-state chemistry in mind. The method is based on an intuitive partitioning scheme for the different kinds of chemical bonding in solids and is thus intended to bridge a gap between (too) simple, classical potential schemes and (too) sophisticated quantum-mechanical strategies. As a consequence, the whole aixCCAD approach needs to be based on crystal-chemical information known to the perceptive experimentalist a priori. aixCCAD's partitioning scheme relies on the bond valence concept, the universal bonding energy-distance relationship, and the concept of absolute electronegativity and hardness; by doing so, aixCCAD offers atomistic simulations of molecular dynamics-type in which the atomic charges are dynamical variables of freedom.

It this does not sound appealing to you, you probably do not originate from solid-state chemistry. For more information, please have a look at our methodology section.

Institute of Inorganic Chemistry
Chair of Solid-State and Quantum Chemistry
Prof. Dr. R. Dronskowski

 RWTH Aachen