MacroModel Reference Manual - ISP

Chapter 4: Operation CodesIMPS — perform IMPortance SamplingNote:IMPS affects the course of MCLO and MCSD simulations. For the full description ofpossible combinations and what they do, see the MacroModel Technical Manual.This command activates the importance sampling option. Use of this command implies that theinput file contains the output from a conformational search. When this command is encountered,all the structures in the input file are read and the values of the specified torsions andbond angles calculated for each conformation. These are used later in the importancesampling. The energy and number of times the structure was found in the conformationalsearch are also read from the input file. These quantities may be used to weight the importancesampling (this last option is not recommended, see below).Importance sampling also activates calculation of conformational populations which can beused to obtain relative free energies (see MDSA command).Importance sampling can be used either as a replacement or in conjunction with MetropolisMonte Carlo (MMC) in both Monte Carlo and mixed mode simulations. The method isdescribed in detail in the technical manual and examples of command files are provided inChapter 10 of the MacroModel User Manual.arg1Frequency of performing IMPS steps0 Perform an IMPS step each time a MMC step is requested.nPerform IMPS step every n times a MMC step is requested and a Metropolis MonteCarlo step the rest of the time.