# General Basis Set Examples

In Spartan it is possible to use other basis sets, and even build your own basis set.
The steps are, in brief:

1. create a basis file
2. put this basis file in an appropriate location
3. add a couple keywords to the option line of Spartan's Calculation Dialogue
4. run the job.
5. Some other relevant points are raised in section 5.
6. Finally, we have some links to sample basis files.
Each is covered in a little more detail in the following discussion.
1. Create a basis file.
Examples of valid basis set files can be found in the auxdir/basis directory (found in Spartan's install directory) and in the final section of this page. The first line should be either
• \$basis
or
• BASIS="name of basis file"
the last line should be either "\$end" or consist of a series of dashes. i.e.
• \$end
or
• -----------------------

The remainder of the file should be recognizable to those who are familiar with the Gaussian basis sets. The best way to understand this is to examine a sample file.

``` ----- Begin Sample Basis File ----- \$basis   H 0   S 2 1.0      1.30976     0.430129      0.233136    0.678914 ****   O 0   S 2 1.0      49.9810     0.430129       8.89659    0.678914   SP 2 1.0      49.9810     0.0494720    0.511541       8.89659    0.9637820    0.612820 **** ----- End Sample Basis File ----- ```

Each atom section begins with a line containing the atomic symbol and is terminated by a line of 4 asterisks (****). The atomic symbol is followed by a set of lines for each atomic shell. The first line of each shell consists of 3 parts;

1. the shell type, one of S,SP,D,F, or G
2. the number of gaussians
3. a scaling number (usually 1.0)
Each gaussian follows with the exponents and then the coefficient. For SP shells the S coefficient comes first followed by the P coefficient.

2. Copy the basis set file to the "correct location".

This should either be your "\$HOME" directory or the .../auxdir/basis/ directory. This file name must be in all capital letters.

3. You will then need to add some keywords to your molecule.
Some useful keywords are:
 GBASIS=FILENAME.BASIS to give the basis set file name PURECART=gfd Controls the use of either pure or Cartesian basis function for g, f and d shells, respectively. 1 indicates pure and 2 Cartesian. PURECART=112 is a common options to make the d orbitals Cartesian, but g and f pure. GUESS=GWH orGUESS=CORE It is possible the default wavefunction guess does not work well with your basis set. One of these might work better. ECP=GEN Required if defining your own ECP.

Note: You may also have add the IGNORESYMMETRY keyword. Symmetry often fails (with messages like "NOSasy bad") for many basis sets.

4. Submit the job.

Note that this is an advanced and unsupported feature. You may get a number of errors, some due to simple mistakes in the options or basis set file. Some due to numerical problems due to our computational programs not being optimized for your basis set. When something bad happens make sure to examine the entire verbose output (as well as the standard terse output) for clues as to what went wrong. Typically the error message at the end of the file is misleading and you may have to page up toward the beginning of the file to see the first printed error.

5. Other important caveats.
• Symmetry is often a problem, you may want to turn it off.
• While energies are possible with f (and g) orbitals, charges and graphical surfaces with these high basis sets (as well as many other electronic properties) are not yet supported.
• Geometry optimization is not available for g orbitals.
• It is very easy to type in wrong values, or enter incorrectly normalized coefficient values. This will lead to some very strange convergence problems, or other seemingly random error messages.
• This feature is not supported by Wavefunction. It is supplied to expert users who are willing to debug their own code.

6. Sample Files Here are three examples of basis set files.
• MYHOBASIS.BASIS : example presented above.
• MIXING.BASIS : showing how to mix standard basis sets.
• ECPEX.BASIS : an example using the ECP functionality.
• gbasis-example.spartan : demonstrate the basis set file (MYOHBASIS.BASIS) listed in this FAQ as well as some other advanced features. (Clicking on this link a water molecule will be opened with the appropriate keywords already set.)

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