OPTIM has now been superceded by OPTIM2. This documentation is maintained only for reference.
OPTIM is a program to locate stationary points on potential energy surfaces and calculate reaction pathways. It was originally based upon the optimizer written for the ACES package[1] by John Stanton. Little of the original code remains, except in the point group analysis routines, which have also been significantly modified. Optimization algorithms now include eigenvector-following, [2,3,4,5,6,7,8] steepest-descent (via the Page-McIver method), conjugate gradient and hybrids thereof. Pathways can be calculated in several ways, and it is also possible to use a `fictitious kinetic' metric, usually referred to as `mass-weighted' coordinates. There is provision to treat rigid body systems; the TIPS family of rigid molecule, effective pair potentials for H2O are known to the program and employ centre-of-mass and Euler angle coordinates. The same eigenvector-following optimizer is now present in the ORIENT3 program, which can treat arbitrary mixtures of atoms and rigid molecules using distributed multipoles to describe the electrostatic energy.[9,10] These optimization algorithms can also be very effective in solving fitting problems, especially if analytic derivatives can be obtained.
The program has analytic first and second energy derivatives coded for dozens of empirical potentials and can also read derivatives from disc so that it can be run iteratively in tandem with ab initio packages. The only file that you must have to start a calculation is odata. Each call to OPTIM performs one or more steps of various kinds; after each call the current state of the calculation is saved in file ARCHIVE (unformatted) and the updated coordinates for every step are saved in order in file points. The coordinates after the final step are also written to file points.final and a new input file for OPTIM based upon this geometry is written to odata.new. This file also contains the energy for the previous step and the point group (if it was evaluated) as COMMENT statements. By default an existing ARCHIVE file in the working directory is ignored. To continue an old run from an existing ARCHIVE file the RESTART keyword must appear in odata.
The master source directory is 1#1wales/opt/OPTIM on dougal.ch.cam.ac.uk.