Basis set

The basis set is defined as a dictionary, where the keys are the types of the basis sets, and the values are the basis set:

basis = Dict("ao"=>"cc-pVTZ",
             "jkfit"=>"cc-pvtz-jkfit",
             "mpfit"=>"cc-pvtz-mpfit")

The basis set dictionary contains three keys: ao, jkfit, and mpfit. The ao key contains the basis set for the AO integrals, the jkfit key contains the basis set for the density fitting integrals in the Hartree-Fock calculations, and the mpfit key contains the fitting basis set for the correlated calculations.

Alternatively, you can define the basis set using a string that defines the AO basis. In this case, the jkfit and mpfit basis names will be generated automatically. Here's an example of how you can define the basis set using a string:

basis = "cc-pVDZ"

Common acronyms are also supported for the basis set names, e.g., cc-pVDZ can be written as vdz, and aug-cc-pVTZ can be written as avtz.

Additionally to the default basis, it is possible to specify basis sets for each element/center:

basis = Dict("ao"=>"avdz; O=avtz; H1=vdz; H2=vtz",
             "jkfit"=>"cc-pvtz-jkfit",
             "mpfit"=>"cc-pvtz-mpfit")

In this case, the basis set for the AO integrals is avdz for all elements, except for oxygen (irrespective of the name in the geometry, i.e., "O", "O1", etc), which uses avtz, and hydrogen, which uses vdz and vtz for the centers named "H1" and "H2", respectively.

Moreover, it is possible to define custom basis sets for each element/center using the Molpro format:

basis = Dict("ao"=>"cc-pVTZ; o=avdz;
             h={! hydrogen
                s, H , 13.0100000, 1.9620000, 0.4446000, 0.1220000
                c, 1.4, 0.0196850, 0.1379770, 0.4781480, 0.5012400
                c, 4.4, 1.0000000
                p, H , 0.7270000
                c, 1.1, 1.0000000}",
             "jkfit"=>"vtz-jkfit",
             "mpfit"=>"avtz-mpfit")

In this case, the basis set for the AO integrals is cc-pVTZ for all elements, except for oxygen, which uses avdz, and hydrogen, which uses a custom basis set. The Fock density fitting basis set is vtz-jkfit, and the fitting basis set for the correlated calculations is avtz-mpfit.

Even-tempered diffuse (or steep) functions can automatically be added to the basis set by specifying the desired number of functions in the basis set definition:

basis = "vdz+steep+2diffuse"

Here, the basis set vdz is augmented with one steep function and two diffuse functions (for each angular momentum). The exponents are calculated as follows:

For the diffuse functions, the exponent is set to $\frac{e_1^2}{e_2}$, where $e_1$ is the most diffuse exponent and $e_2$ is the second-most-diffuse exponent in the angular shell.
If there is only one exponent in the list, the new exponent is set to $\frac{e_1}{2.5}$.
For the steep functions, the exponent is set to $\frac{e_1^2}{e_2}$, where $e_1$ is the steepest exponent and $e_2$ is the second-steepest exponent in the angular shell.
If there is only one exponent in the list, the new exponent is set to $e_1 \times 2.5$.

This works also for explicitly defined basis sets. In this case +diffuse or +steep can be added after the curly brackets.

ElemCo.BasisSets — Module

BasisSets

Module for working with basis sets.

The basis set is stored in the BasisSet instance. The basis set can be generated using the generate_basis function.

Basis set

Exported functions and types

Internal functions and types