basis

This option defines the basis functions used for quantum chemistry calculations. You can define basis sets in several flexible ways.

• Using Built-in Basis Sets
• Explicit Basis Set Definitions
• Using Self-defined Basis Set Files
• Define Different Basis Sets for Different Elements

Using Built-in Basis Sets

A lot of important basis sets have been provided in a directory basis in the same path of Qbics. The files are named after their names well-known in computational chemistry community. For example, basis/cc-pvdz contains the cc-pVDZ basis. All files are named in small cases.

To use them, simple write down the basis set name. It is case-insensitive. For example, to use def2-TZVP for all atoms:

basis
  def2-TZVP
end

Qbics will extract basis set information from basis/def2-tzvp.

Explicit Basis Set Definitions

You can also explicitly define your own basis sets. For example, your system contains two atoms, H and Li, then their basis sets can be defined in this way:

basis 
  H     0
  S   3   1.00
        13.0107010             0.19682158E-01
        1.9622572              0.13796524
        0.4445379              0.47831935
  S   1   1.00
        0.12194962             1.0000000
  P   1   1.00
        0.8000000              1.0000000
  ****
  Li     0
  S   5   1.00
        266.27785516           0.64920150325E-02
        40.069783447           0.47747863215E-01
        9.0559944389           0.20268796111
        2.4503009051           0.48606574817
        0.72209571855          0.43626977955
  S   1   1.00
        0.52810884721E-01      1.0000000
  S   1   1.00
        0.20960948798E-01      1.0000000
  P   2   1.00
        1.4500000              0.2586000
        0.3000000              1.0000000
  P   1   1.00
        0.0820000              1.0000000
  ****
end

The basis set definition is of standard Gaussian94 format:

• The definition of the basis set for each atom ends with 4 asterisks, i.e. ****.
• The definition starts with the element name like Li and a 0. Currently 0 has no meaning.
• Then, each GTO shell is defined. The shell definition starts with three parameters:

• Angular momentum. It can be any nonnegative numbers like 0, 5, or one of S, P, D, F, G, H, and I.
• Contraction degree. It must be a positive integer.
• A real number. Currently it has no meaning.
• Then, each line defines the exponent and contraction coefficient of the primitive GTO to be contracted. They are 2 real numbers.

Using Self-defined Basis Set Files

You can also put your explicit basis set definitions into some files, say /home/zhang/userdef/my-own-basis. Qbics will automatically read it if you give explicit file name including path.

basis
  /home/zhang/userdef/my-own-basis
end 

Define Different Basis Sets for Different Elements

If you want to use different basis set s for different elements, then you can write element in the first line, then write element and basis set file name line by line. For example:

basis
  element # This indicates that Qbics will assign basis set element by element.
  O aug-cc-pvtz
  C cc-pvdz
  N /home/zhang/userdef/my-own-basis
end