Towards uncontracted basis sets in Density Functional Theory

From the standpoint of quantum calculations, contracted Gaussian orbital basis sets have proven useful for very accurate Hartree-Fock, Density-Functional and high-level quantum solutions [1]. Still today there are times when inaccuracies in calculations are incorrectly attributed to a lack of polarization functions rather than strong ionicity effects. Further, it is recognized that greater accuracy could be achieved by removing the constraint of contracted orbitals. To this point, we have developed an automated approach to remove inaccuracies due to contracted orbitals. This work proceeds through the use of an advanced automated calculation for efficient optimization in which separate environmentally informed contractions are used for each and every atom in the molecule. The result is a machine generated code for basis optimization which is applicable to any type of molecular/atomic orbitals.   We present results on diatomic molecules and the SF₆ molecule and discuss strategies for deciding one whether to optimize on an iteration-by-iteration basis or at the end of each single-point calculation.

[1] Porezag, Dirk and Pederson, Mark R, Phys. Rev. A, 1999