MacroModel Reference Manual - ISP

Chapter 4: Operation Codes4.7 Constrained Energy MinimizationDRIV — carry out a geometry DRIVeWhen included in a BGIN/END loop the DRIV command drives the specified geometric parameterthrough a set of fixed values. The parameter can be a dihedral angle, a bond angle, or abond distance. The DRIV command should be followed by a MINI (not an ELST) to evaluatethe energy. The driving process involves adjusting the specified geometric parameter to thestarting value and then setting a constraint with a large force constant (1000 kJ/mol) for thatparameter. Then an energy minimization is carried out, and in the next pass through the BGIN/END loop the parameter is incremented by the value of arg7 and the process repeated. When thefinal value of the parameter (arg6) is reached or surpassed then a “grid” of energy values iswritten to a .grd file. This grid can be displayed as a contour map in Maestro (see Section 8.3of the MacroModel User Manual); its format is described in Appendix F.You can have two consecutive DRIV commands to select two geometric parameters. You mustspecify the same type of parameter for each command: one angle and one distance is not anallowed combination. The inner loop runs over the parameter specified by the second DRIVcommand. Two DRIV commands are needed to calculate data for a Ramachandran-type plot.Note: This opcode is incompatible with the use of DEBG 23.arg1-4arg5arg6Atom numbersThese define the geometric parameters to be driven. They must be valid atom numbersin the filename.mae file For dihedral angles they must also define an angle thatis rotatable, i.e., not one in which the four atoms lie in a ring. The geometric parameteris determined as follows:• If arg3 and arg4 are zero, the distance defined by arg1 and arg2 is driven.• If arg4 is zero, the angle defined by arg1, arg2 and arg3 is driven.• If arg1–arg4 are non-zero, the dihedral angle defined by arg1–arg4 is driven.Starting valueThis does not need to be the current value in the filename.mae file as MacroModelwill first set the parameter to the required value. Must be nonzero for distancedriving.Final valueThe drive finishes when the parameter is greater than or equal to this value if arg7 ispositive, or when the parameter is less than or equal to this value if arg7 is negative.MacroModel 9.7 Reference Manual 63