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2.4 Optimization
2.4.1
Force Field Options
Force field options (currently just the van der Waals cutoff), are available in the menubar under
Optimize→Force Field→Options, see Figure 2.45. The force fields in PQSMOL do not have an Ewald summation (or
equivalent) of all pair-wise van der Waals interactions; instead there is a simple cutoff (default 10 Angströms) beyond which
the van der Waals terms are simply neglected. This value can be changed here.
Figure 2.45: Force Field Options window
2.4.2
Optimization Options
There are several optimization options available, Figure 2.46.
Figure 2.46: Optimization options
• Steps sets the number of optimization cycles (default 500)
• GTOL sets the convergence criterion for the root mean square gradient (default 0.0003)
• ETOL sets the convergence criterion on the change in energy from the previous cycle (default 10−6 )
• Print Flag sets the verbose output level (for debugging only)
• Calculate Hessian calculates a starting Hessian matrix for the Sybyl5.2 force field only (there is no effect for the
Universal force field)
• Optimization Animation update sets the number of cycles between geometry updates to the Build window.
Setting this option to a value of 1 will cause a structure geometry update on every optimization cycle. A value of 0
will turn off optimization animation.
If both the GTOL and ETOL convergence criteria are satisfied or the maximum number of optimization cycles Steps
has been exceeded, the optimization will stop. In line with similar criteria in the PQS program, GTOL and ETOL are
measured in atomic units.
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PQSMol Manual