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The Theory of Intermolecular Forces


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Orient is a program for carrying out calculations of various kinds for an assembly of interacting molecules. It uses a site-site potential specified by the user, including electrostatic, induction, repulsion, dispersion and charge-transfer interactions if required.

The electrostatic interactions may be described by simple point charges or by more elaborate descriptions involving distributed multipoles up to rank 5 if required. The electrostatic potential of a multipole model molecule can be displayed on a surface around the molecule.

Distributed polarizabilities may be used, and the induction energy can be calculated at first order or iterated to convergence.

The site-site repulsion and dispersion and charge-transfer terms may be anisotropic.

The energy of the assembly can be calculated at specified configurations, or the geometry can be optimized to find minima and transition states and the paths between them. The basin-hopping procedure can be used to find local minima and the global minimum.

Molecular dynamics and Monte Carlo calculations can be performed on the assembly. The program can calculate pressure and dielectric second virial coefficients, including quantum corrections to the pressure virial coefficient.

The program can also be used to study interactions involving ionic or molecular crystal surfaces. Clusters of molecules or periodic adlayers adsorbed on the surface can be defined, and their geometries optimized. Monte Carlo calculations can also be performed on the adsorbed cluster or adlayer. The top layer of the crystal can be treated as an adlayer, and its structure optimized to study surface reconstruction effects. The interaction between the surface layer and the body of the crystal also provides a tool for studying crystal growth morphology using the attachment energy and related quantities.

The Orient program manual gives full details and is available for download in PDF format.

The program is available for non-commercial academic use free of charge. Please complete the licence application form if you wish to use it. On receipt of your application we will send authorization details to allow you to download Orient.

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