mirror of
https://github.com/cp2k/cp2k.git
synced 2026-07-27 13:45:19 -04:00
103 lines
4.2 KiB
Markdown
103 lines
4.2 KiB
Markdown
# Basis Sets
|
|
|
|
In CP2K's {term}`Quickstep` module, the Kohn-Sham orbitals are expanded in atom-centered Gaussian
|
|
basis functions. This is different from pure plane-wave codes: increasing the real-space grid
|
|
[CUTOFF](#CP2K_INPUT.FORCE_EVAL.DFT.MGRID.CUTOFF) improves the auxiliary plane-wave representation
|
|
of densities and potentials, but it does not by itself reach the complete basis set limit. For
|
|
systematic convergence, the Gaussian basis quality and the grid parameters have to be considered
|
|
together.
|
|
|
|
Basis sets are selected for each atomic [KIND](#CP2K_INPUT.FORCE_EVAL.SUBSYS.KIND). The files that
|
|
contain the basis definitions are listed in
|
|
[BASIS_SET_FILE_NAME](#CP2K_INPUT.FORCE_EVAL.DFT.BASIS_SET_FILE_NAME). CP2K searches these files in
|
|
the current directory and in the configured CP2K data directory.
|
|
|
|
```text
|
|
&FORCE_EVAL
|
|
&DFT
|
|
BASIS_SET_FILE_NAME BASIS_MOLOPT
|
|
&END DFT
|
|
&SUBSYS
|
|
&KIND O
|
|
BASIS_SET DZVP-MOLOPT-GTH
|
|
&END KIND
|
|
&KIND H
|
|
BASIS_SET DZVP-MOLOPT-GTH
|
|
&END KIND
|
|
&END SUBSYS
|
|
&END FORCE_EVAL
|
|
```
|
|
|
|
## Basis Set Names
|
|
|
|
Many CP2K basis sets encode their purpose in the name:
|
|
|
|
- `SZV`, `DZVP`, `TZVP`, `TZV2P`, and `QZVPP` indicate increasing basis quality.
|
|
- `MOLOPT` basis sets are molecularly optimized Gaussian basis sets commonly used with GPW.
|
|
- `SR` indicates short-range MOLOPT variants. They are less diffuse and often more efficient for
|
|
large condensed-phase systems when the target property does not require diffuse functions.
|
|
- `GTH` basis sets are intended for GTH pseudopotential calculations.
|
|
- `q1`, `q4`, `q6`, and similar suffixes indicate the number of valence electrons represented by the
|
|
matching pseudopotential.
|
|
- `ae` basis sets are all-electron basis sets, commonly used with the GAPW method and
|
|
`POTENTIAL ALL`.
|
|
|
|
For production calculations, use basis sets and pseudopotentials that were designed to work
|
|
together. For example, `DZVP-MOLOPT-GTH` for oxygen is normally paired with `GTH-PBE-q6` in a PBE
|
|
calculation, while UZH protocol basis sets from `BASIS_MOLOPT_UZH` are paired with corresponding
|
|
entries from `POTENTIAL_UZH`. For new GPW production inputs, these UZH protocol pairs are the
|
|
preferred starting point where available; the older MOLOPT/GTH libraries remain useful for
|
|
compatibility and comparison with established inputs. The same `BASIS_MOLOPT_UZH` file also contains
|
|
all-electron MOLOPT basis sets for GAPW simulations, such as `SVP-MOLOPT-GGA-ae`,
|
|
`TZVPP-MOLOPT-GGA-ae`, and `QZVPP-MOLOPT-GGA-ae`, to be used with `POTENTIAL ALL`.
|
|
|
|
## Basis Set Roles
|
|
|
|
The keyword [BASIS_SET](#CP2K_INPUT.FORCE_EVAL.SUBSYS.KIND.BASIS_SET) can carry an optional basis
|
|
type. Without an explicit type, CP2K uses the primary orbital basis:
|
|
|
|
```text
|
|
&KIND O
|
|
BASIS_SET ORB DZVP-MOLOPT-GTH
|
|
&END KIND
|
|
```
|
|
|
|
This is equivalent to the more common short form:
|
|
|
|
```text
|
|
&KIND O
|
|
BASIS_SET DZVP-MOLOPT-GTH
|
|
&END KIND
|
|
```
|
|
|
|
Other basis roles are used by specific methods, for example:
|
|
|
|
- `AUX_FIT` for the auxiliary density matrix method.
|
|
- `RI_AUX` for resolution-of-the-identity correlation methods.
|
|
- `LRI` for local resolution-of-the-identity approaches.
|
|
|
|
The method-specific documentation usually states which auxiliary basis is required.
|
|
|
|
## Convergence and Practical Choices
|
|
|
|
Start with a basis set that is appropriate for the target accuracy, then converge the grid
|
|
parameters. For many routine condensed-phase GPW calculations, double-zeta or triple-zeta MOLOPT
|
|
basis sets are common starting points. For new setups, first check whether a matching UZH protocol
|
|
basis and pseudopotential pair is available. Accurate energy differences, weak interactions,
|
|
response properties, and post-Hartree-Fock methods may require larger or more specialized basis
|
|
sets.
|
|
|
|
Diffuse basis functions can improve accuracy for molecular anions, excited states, polarizabilities,
|
|
and weak interactions, but they also increase the cost and may make the overlap matrix more
|
|
ill-conditioned. In periodic calculations, diffuse functions can also increase the number of
|
|
periodic images that have to be considered.
|
|
|
|
For a simple tested example, see [](../../getting-started/first-calculation).
|
|
|
|
## See Also
|
|
|
|
- <https://en.wikipedia.org/wiki/Gaussian_orbital>
|
|
- <https://www.cp2k.org/basis_sets>
|
|
- <https://www.cp2k.org/tools:cp2k-basis>
|
|
- [](#VandeVondele2007)
|
|
- [](#Iannuzzi2026)
|