MacroModel Reference Manual - ISP

Chapter 4: Operation Codesarg7V 3 (positive number gives staggered minima)MCSM — Monte Carlo Single MinimumThis procedure is similar to that described by Li and Scheraga [38] and is a global search forthe single lowest energy structure. The search can be conducted with or without minimization(depending on arg3). While this method is good at finding a single low energy conformer, thereis no guarantee that it will locate the true global minimum energy conformer.Monte Carlo internal coordinate conformational search is performed with minimizations on asingle structure. Variable internal coordinates are specified by TORS and/or MOLS.MCSM can be used with cyclic structures providing that either ring bonds are not varied or thatring closure commands (RCA4) are used for each ring in which variable torsions are used.During the run, random variations will be applied to 2-4 randomly selected dihedral anglesfrom the TORS lists or molecular translations/rotations from the MOLS lists for each MonteCarlo step. If some other range of variable coordinates is desired, the range is set with theMCNV command.If used within a BGIN/END loop, all structures in the input file will be read and the globalminimum found will be listed to the output file at the end of every MC iteration set for eachinput structure. The ultimate global minimum would be found by examining the energies ofeach of the output structures.Unlike MCMM, MCSM requires no MINI command. It must appear after a READ command.In general, Monte Carlo searches should use CHIG commands to maintain all chiral centersand TORC commands to hold double bond geometries constant. If chirality or double-bondgeometry is lost in any step, then following steps will be wrong if the resulting geometry isused for subsequent steps.arg1Minimization mode0 Steepest descent.1 PR conjugate gradient (best general method).3 Variable Metric (not recommended with MCSM).4 Full matrix NR (not recommended with MCSM).9 TNCG (good for flexible structures).108MacroModel 9.7 Reference Manual