MacroModel Reference Manual - ISP

Chapter 4: Operation Codesarg1 Atom 10 Clear all existing FXTA constraintsarg2-4 Atoms 2-4arg5arg6V 1 Force constant (default = 1000 kJ/mol)Desired torsion angle, in degrees>360 The initial value will be used.arg7Half-width of flat bottom in degrees0 A standard 1-fold cosine well will be used.arg8Multiplicity>1 Allows specification of several allowed ranges for the same set of torsion angles,using a method described by Sefler et al. [26]. If arg8 is two, for example, rangesaround two dihedral angles can be specified in order to enforce constraints obtainedfrom analysis of NMR coupling constants by means of the Karplus equation. In thisexample, two FXTA commands are expected for the same values of arg1-4. For eachsuch FXTA command, you should specify a desired central position in arg6 and aflat-bottom half-width in arg7. When the last specification is read for a given atomset (for example, when the second FXTA interaction is read for an atom set with anarg8 value of two), MacroModel resets the central angles and half-widths for the setto values that achieve your original input specification. DEBG 14 makes this visible.FXCO — FiX COnstraintsGenerates a series of FXTA torsional constraints with flat bottoms to hold the input structure inits starting conformation. This opcode must come after any SUBS opcodes that are present andafter the READ opcode that reads the structure for which these constraints are to be generated.arg1Mode selection0 FXTA for all torsions.1 FXTA for all but double bonds.2 FXTA for all but bonds between sp 2 atoms.72MacroModel 9.7 Reference Manual