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.
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.Rou change only the defaults; they are overridden by anything specified in the route section of an input file. Thus, if the Default.Rou 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.
Not all route section keywords are honored in the Default.Rou 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.
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.
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:
-S- EXPCONS
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 1 GB of memory, more memory should be given to each job:
-M- 64MW -#- MaxDisk=10GB