Format of MacroModel .grd Files

Files with a .grd suffix are produced by the DRIV command. These files are used by Maestro to create contour plot displays.

Although right now Maestro and DRIV support two-dimensional data, the file format is designed to accommodate three dimensional data sets. The format is as follows. Fortran format descriptors are given for each part of the file. This file format is based on the Gaussian-90 electron-density file format.

Line 1: Format (A80). In general, this can contain any string, and can be used as a title line; however, if this line contains the string BMIN in the columns 1-4 followed by a list of atom numbers in (4I5) format, Maestro will attempt to display the molecule in file filename-out.mae, where filename is the prefix of the .grd file, and will use the atom numbers to associate the contour display with the torsion.

Line 2: Format (A80). As for line 1. The atom numbers define the second dihedral which was driven during the calculation.

Line 3: Format (I5,3F12.6). Natoms, X-Origin, Y-Origin, Z-Origin. Natoms is the number of atoms in the molecule. The X-Origin and Y-Origin variables define the axis values of the “origin” (bottom left) of the contour plot. These will be taken from the starting angles in the DRIV command; for example, they might both be −180.0.

Lines 4-6: Format (I5,3F12.6). Ninc, Xinc, Yinc, Zinc. Each of the three lines is for one driven angle. Ninc is the number of increments of the angle and Xinc, Yinc, and Zinc are the components of an increment along the axes of the first, second, and third driven angle. Since for DRIV-generated data the angles are driven separately and independently, and since we now support only the two-dimensional case, lines 4-6 should have the following form:

   NN  NN.NNNNNNN    0.000000    0.000000
   NN    0.000000   NN.NNNNNN    0.000000
    0    0.000000    0.000000    0.000000

NN is the number of increments of the angle and NN.NNNNNN is the size of an increment.

There next follow Natoms lines, starting with line 7. Each line has format (I5, 4F12.6), and the variables are atomic number, charge, and X, Y, and Z coordinates. These lines are actually ignored by MacroModel, but must be present.

Starting with line (7 + Natoms), the energetic data corresponding to the grid points are given, one energy value per line, in (F12.6) format. The energies are ordered so that the index corresponding to the last angle moves fastest, and the index corresponding to the first angle moves slowest. So, for a two-dimensional data set with the energies in an array called E, the sequence of the energies would be E(1,1), E(1,2), ..., E(1,Ninc2), E(2,1), E(2,2), ..., E(2,Ninc2), ..., ..., E(Ninc1,1), E(Ninc1,2), ..., E(Ninc1,Ninc2). Thus, there are a total of Ninc1* Ninc2 energy values.

If for some reason an energy calculation for one of the points failed, the energy is replaced with the text skip.This instructs the Maestro plotting program to skip that point.