:orphan:
Pick the right basis for your calculation
=========================================
The development of basis sets suitable to use in relativistic calculations
reflects the relatively lateness of the field's development. Because the more
consistent efforts in method development started at about the mid 1980's, it
wasn't until well into the late 1990's that the pioneering works of the early
and mid 1990's were substantially complemented and improved upon.
This situations has dramatically improved in recent years, notably with the work
of K. G. Dyall, and Dirac users are strongly advised to use Dyall's basis sets
whenever they are available. These sets follow roughly the
"correlation-consistent" philosophy introduced by Dunning and coworkers
:cite:`Dunning1989`, so they already contain polarization functions, but the SCF sets
are designed for an adequate SCF representation rather than to match correlating
sets for the valence shells.
Dyall basis sets
----------------
We recommend that you use the `Dyall basis set
repository `_
whenever they are available for the elements of interest.
In order to make that usage as convenient as possible,
the following files, containing all sets currently available at the
URL above (published or to be published), are made available:
+------------------+-------------+----------------+----------------+-----------+
| quality | valence | core-valence | all-electron | DFT |
+==================+=============+================+================+===========+
| double-zeta | dyall.v2z | dyall.cv2z | dyall.ae2z | dyall.2zp |
+------------------+-------------+----------------+----------------+-----------+
| triple-zeta | dyall.v3z | dyall.cv3z | dyall.ae3z | dyall.3zp |
+------------------+-------------+----------------+----------------+-----------+
| quadruple-zeta | dyall.v4z | dyall.cv4z | dyall.ae4z | dyall.2zp |
+------------------+-------------+----------------+----------------+-----------+
While the division in "valence" and "core-valence" can be at times not so
clear-cut as for lighter elements, the option was made to stick to the usual
jargon of non-relativistic theory, particularly in relation to the
"correlation-consistent" family of basis sets.
The valence basis sets are defined to include functions for correlation of the
outer ns shell and the (n-1)s and p shells for the s elements, the outer ns and
np shells for the p elements, the ns, np, nd, and (n+1)s for the d elements, and
the ns, np, nd, nf, (n+1)s, (n+1)p, (n+1)d, and (n+2)s for the f elements. The
choice for the f block of these is necessary to cover correlation of the open f
shell, which becomes a semicore shell towards the end of the row.
The core-valence basis sets include the (n-2) shell for the s elements, the
(n-1) shell for the p elements, the (n-1) shell for the d elements, and nothing
extra for the f elements.
The all-electron basis sets include correlating functions for all shells, down
to the 1s for all elements. These are intended for use when correlating all
electrons.
The DFT basis sets do not contain the correlating functions as these are not
necessary for DFT (or Hartree-Fock) calculations. With inclusion of all required
polarization functions they are the most economical choice for DFT calculations.
Users are encouraged to look in these files and in the original archives
published at Theor. Chem. Acc. (as, for instance, for the `5p TZ basis
`_ to get a feel for
what is included in each case.
In the case of p-block elements, additional files containing the
corresponding diffuse functions, in addition to the valence and
core-valence basis sets mentioned above, are also provided.
+------------------+--------------+-----------------+
| quality | valence | core-valence |
+==================+==============+=================+
| double-zeta | dyall.av2z | dyall.acv2z |
+------------------+--------------+-----------------+
| triple-zeta | dyall.av3z | dyall.acv3z |
+------------------+--------------+-----------------+
| quadruple-zeta | dyall.av4z | dyall.acv4z |
+------------------+--------------+-----------------+
With the recent addition of Dyall basis sets for the light elements, it is no
longer necessary to use the standard non-relativistic basis sets, such as the
correlation-consistent sets of Dunning and coworkers. However, because the
Dyall basis sets are quite a bit larger, you might want to continue using these
basis sets. It is advisable that, in order to have a balanced description when
light and heavy elements are present, that one uses either contracted or
uncontracted sets thoughout.
See the `Dyall basis set
repository `_
for the latest updates by Ken Dyall and the appropriate basis set
references. In case of errors or omissions on any of the files in this directory,
users are kindly asked to contact the authors of DIRAC.
Other relativistic basis sets
-----------------------------
Apart from Dyall's sets, one can choose several different basis sets based upon
geometric progressions of exponents. One such set is that of K. Faegri, also
available in the basis set library, but with the drawback that the user needs
to extend it by adding polarization functions.
Non-relativistic and scalar-relativistic basis sets
---------------------------------------------------
The DIRAC distribution shares a large library of standard
non-relativistic and scalar-relativistic basis sets with the
`Dalton `_ program.
These basis sets can be found
in the directory **basis\_dalton** of the DIRAC distribution.
These basis sets are not all suitable for relativistic calculations,
especially not for the heavier elements.
Basis sets developed for full relativistic calculations (including
spin-orbit coupling) can be found in the directory **basis**.