Grid Calculation

The GRID calculation is the two-dimensional analog of the PATH calculation. In a PATH calculation, one coordinate is flagged with a '-1'. In a GRID calculation, two coordinates are flagged by '-1's. An example of a GRID calculation is shown in the Figure. Note that the keywords STEP1=n.nn and are essential.

Figure: Example of a GRID Calculation
Water, potential energy surface for
 O   0.92 -1     0  0    0 0   1
 H   0.92  0   104 -1    0 0   2 1
 2 1 3

In this example, the potential energy surface for water is generated. For one axis of the 2-D plot, the O-H bond length is varied from 0.92Å to 1.02Å, in 11 steps of 0.01Å, and in the other axis, the H-O-H angle is varied from 104 to 114$^{\circ}$ in 11 steps of 1.0 degree. Because of the use of symmetry, there are no variables to be optimized. If symmetry were not used, then the second O-H bond length could either be optimized, by setting its flag to 1, or held constant, by setting its flag to 0.

Keywords used with the GRID option are POINT1=n and POINT2=m: to use n and m points in directions 1 and 2; and keywords to specify how the geometry should be optimized. n x m should be less than 400000