Steric

A Program to Calculate the Steric Size of Molecules about a Point in terms of their Cone Angles and Solid Angles, as well as their total Volumes and Projected Areas



This program was originally written to calculate the solid angle represented by a molecule as seen from a point perspective according to a semi-analytical algorithm developed by White et al. (1993). Since then, not only has the semi-analytical algorithm undergone major changes (Taverner (1996)) to incorporate atomic overlaps of order greater than two, but several other calculations have been added. The original Cone Angle concept by Tolman has been incorporated. Vertex angle and Solid angle of bonded and non-bonded regions of overlap have been included. A fully numerical Solid angle can also be calculated, together with a fully numerical molecular volume. The molecular volume is not the only parameter, however, that is not dependent on a point of perspective. The new fully analytical molecular projection area is not dependant on a point perspective, but is dependant on a directional perspective. All the other calculations are applicable only to situations where the steric size of the molecule about a point is of interest.
Examples of such situations are: Examples where the molecular volume is of interest: Examples where the molecular orthogonal projection area is of interest: Further extensions to the above calculations were added with the radial profile calculation and the conformer average calculation. The radial profile calculation calculates the solid angle (or alternative steric parameter) of the intersection between the molecule and a sphere of a particular radius about the point of perspective. This is performed for a range of radii normally encompassing the entire molecule. Two examples of this are given here, in which two solid angle calculations are compared:

Example Plots from Steric Calculations
Clicking on an image gives a medium sized blow-up
Clicking on a lable gives a large blow-up
Contour Plot of CH3 Perpsective CH3 Orthogonal Benzene
Radial Profiles Multiple Overlap versus
Double Overlap Solid Angles
Close up of PPh2Me PPh2Me



The conformer average involves taking the molecular conformer data from a large set of conformers generated using another program and calculating their steric sizes. The conformer average itself is obtained from a weighted average, the weights being calculated from the energies obtained by the conformer program. This calculation can be performed on all steric parameters, including numerical volume, whereas the radial profile cannot be performed on the volume, for obvious reasons.
Steric is available in binary for Linux (1.2.8), IRIX (5.2) and 32-bit extended DOS (gjgpp) and in source code for other unix platforms. These can be downloaded as a single file from here:

Archive of the steric software directory: steric-directory.tgz

Note that .tgz is the extension of the archive format typically used in Linux. Winzip, Winrar and 7-zip all know how to work with this format.



This program was written by Brian Craig Taverner (craig@hobbes.gh.wits.ac.za).

The last paper to be accepted is on the multiple overlap algorithm. It is available in HTML and other formats