Gaussian 03 Online Manual
Last update: 29 September 2006

Depending on the characteristics of a particular computer system, it is sometimes necessary for performance reasons to override some of the defaults built into the program. This can be done by creating a site customization file. On Unix systems, this file is named Default.Route, residing in $g03root/g03. Under Windows, the Gaussian defaults file is Default.Rou, and it is located in the Gaussian 03W scratch subdirectory (e.g., C:\G03W\scratch). The format of the file is the same on all computer systems.

The following subsections describe the types of information which can be supplied in the defaults file.

Route Defaults

These parameters are introduced by -#- and have the same form as normal route section commands. For example, this line will set the default SCF algorithm to the conventional (non-direct) algorithm:

-#- SCF=Conventional 

There may be more than one -#- line in the file.

Commands listed in Default.Route change only the defaults; they are overridden by anything specified in the route section of an input file. Thus, if the Default.Route contains:

-#- MP2=NoDirect 

and the route section contains the MP2 keyword, then the conventional MP2 algorithm will be used. However, if the route section contains the MP2=Direct keyword, then the direct algorithm will be used.

All sites will want to specify the amount of scratch disk space available via the MaxDisk keyword in the Default.Route file. For example, the following line sets MaxDisk to 800 MB:

-#- MaxDisk=800MB 

This line will have the effect of limiting disk usage in the semi-direct algorithms to the specified amount. Some suitable limit should be defined for your configuration. Keep in mind that the more disk space is available, the faster the evaluation, especially for MP2.

Default.Route Limitations

Not all route section keywords are honored in the Default.Route file. In general, the rule is that only options which do not affect the outcome of a calculation (i.e., do not change the values of any predicted quantities) are allowed in the file. Thus, SCF=Conven, which changes only the integral storage algorithm, will be honored, while Int(Grid=3), which affects the results of many kinds of calculations, will be ignored.

Memory Defaults

It is often the case that Gaussian jobs which unwisely use excessive memory can cause severe difficulties on the system. The -M- directive enforces a default dynamic memory limit. For example, the following line sets default memory use to 32 MB:

-M- 4000000 

Note that this limit can be bypassed with the %Mem Link 0 command. The value may also be followed by KB, MB, GB, KW, MW or GW to indicate units other than words. The default memory size is 6 MW.

Number of Processors

If your computer system has multiple processors, and parallel processing is supported in your version of Gaussian, you may specify the default number of processors to use in the Default.Route file. For example, the following command sets the default number of processors to 4:

-P- 4 

Normally, the program defaults to execution on only a single processor. The %NProcShared Link 0 command can be used to override the default for a specific job. Clearly, the number of processors requested should not exceed the number of processors available, or a substantial decrease in performance will result.

Site Name

The site name may be specified by the directive, which sets -S- as the site name to be used in archive entries generated by Gaussian. The default site name is GINC. For example, the following line sets the site name to EXPCONS:


Typical Default Settings

Here are reasonable default settings for various machine configurations:

  • For a small workstation with 64 MB memory and 1 GB of disk, the default algorithms and memory allocation are fine. MaxDisk is all that need be specified.

      -#- MaxDisk=400MB 
  • On a powerful workstation with 8 processors and 1 GB of memory, being used for large jobs, all 8 processors should be used by default. Also, more memory should be given to each job:

     -M- 64MW
     -P- 8
     -#- MaxDisk=10GB 

User Defaults Files

Gaussian users may set their own defaults by creating their own Default.Route file. Gaussian checks the current working directory for a file of this name when a job is initiated. Settings in the local file take precedence over those in the site-wide file, and options specified in the route section of the job take precedence over both of them.