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553. ZMAKER:Z-Matrix Generation from Cartesian
Coordinates
by Ronald M. Jarret and Joseph C. Veniero, Department of Chemistry, College of the Holy Cross, Worcester, Massachusetts 01610 The ZMAKER program converts the Cartesian coordinates (of four or more atoms) to internal coordinates (distance, angle, torsional angle) and represents the atomic positions within the molecule with a Z-matrix. The coordinates can be read in from a file (with x y z atom-type columnar format) or entered directly. If typed in, the coordinates are written to a file (with the appropriate input format) for future use. The program also has lines of COMMENTed code which allows direct use of COORD (TRIBL) format input files. Editing the program to remove the COMMENT symbols in this labeled section will activate this option. After the coordinates are established, the user is prompted for atom selection from a displayed list to initiate the matrix. No special order of atom number selection is necessary; the program renumbers atoms in accord with the order they are called upon. The remaining unidentified atoms are then displayed for selection of the second atom; a distance is computed relative to the first atom selected. The list of unidentified atoms is again displayed, and the third atom is chosen; values for the 3-2 distance and 3-2-1- angle are calculated. The list of remaining available atoms is displayed, and the fourth atom is selected; values for the 4-3 distance, 4-3-2 angle, and 4-3-2-1 torsional angle are calculated. After an atom is completely defined relative to previous entries, the internal coordinates are displayed, and approval is required before definition of the next atom is possible. If the entry is discovered to be wrong, it can be re-entered at this point (only). This cycle continues until all atoms have been selected and defined relative to other atoms in terms of distance, angle and dihedral angle. Once all atoms have been specified, the program searches for identical internal coordinates (within a set tolerance) and queries the user to establish if each pair is related by symmetry. If so, the same variable will be assigned to the two positions of the Z-matrix; otherwise, separate variables are assigned. The tolerances are defined in the beginning of the program and can be easily altered by editing the program; the initial values are T1= 0.0005 (bond), T2 = 0.05 (angle), T3 = 0.1 (torsional angle). With the symmetry constraints established, a variable filled Z-matrix (compatible with GAUSSIAN 82) is then written to a command file, as are the variable definitions and headers necessary for the execution of a calculation by GAUSSIAN 82. The command file can be readily edited to modify headers, etc. for compatibility with particular operating systems; alternatively, the write statements in ZMAKER can be removed or edited to produce the desired output. NOTE: This system will only be of use on a VAX with a PASCAL compiler. PACSAL (VAX/VMS) Lines of Code: 927 |