Large All-electron Basis Research Articles

Polarization consistent basis sets using the projector augmented wave method: a renovation brought by PAW into Gaussian basis sets.

A recently introduced framework incorporating the Projector Augmented Wave method and Gauss-type function (GTF-PAW) [X.-G. Xiong and T. Yanai, J. Chem. Theory Comput., 2017, 13, 3236-3249] opens alternative possibilities for performing low-cost molecular computational chemistry calculations. In this work, we present our first attempt to expand the applicability of this method by developing a family of compact general contracted polarization consistent basis sets (PAW-Ln) as an optimized GTF basis in combination with PAW. The results show that PAW-Ln, despite having small numbers of primitives, can provide not only better performance than effective core potential (ECP) but also good accuracy and desirable systematic convergence compared to larger all-electron basis sets. This demonstrates that GTF-PAW using the PAW-Ln basis sets could be a better alternative to both conventional all-electron- and ECP-based approaches for routine DFT calculations.

Structure and ionization energies of some analogues of iron-only hydrogenases studied by density functional theory methods

Density functional theory calculations using both the B3LYP and BP86 functional in conjunction with a medium and large size basis set have been used to predict the structures and ionization energies of 12 models of iron-only hydrogenases. Although the structural predictions do not allow a clear discrimination between the different computational models, these models do yield significantly different adiabatic and vertical ionization energies. The closest agreement with experiment is given by the BP86 functional and the large all-electron basis. At this level of theory the adiabatic ionization energies are very close to experiment, but the vertical values are uniformly too small, leading to an underestimation of the reorganization energies. The calculations also suggest that measured ionization energies may help in identifying both the bridge-head group and whether CO bridging takes place upon ionization.

Comparison of ab initioMODPOT interaction energy components against large basis set MBPT (4) calculations for nitromethane dimer

Ab-Initio MODPOT SCE calculations using our own optimized well-balanced minimal basis sets have little basis set superposition error (BSSE) and have proven over the years to give reliable intermolecular geometries and interaction energies. Another approach, using ab initio potential functions from energy partitioned ab initio calculations, has also yielded reliable interaction energies and intermolecular geometries, including crystal structures. We used both of these techniques in comparing the results of a published large all-electron basis set calculation on the nitromethane dimer with the above methods. Our SCF intermolecular minimum energy was at the same internuclear distance as the large all-electron basis set. Our SCF interaction energy, corrected for BSSE, was only 0.4 kcal above the SCF energy of the large basis set SCF calculation corrected for BSSE. We also calculated the energy partitioned components with our ab initio MODPOT basis set and with the larger all-electron basis set and showed that the small difference in interaction energy was due to a small difference in the first-order electrostatic multipolar term. (We also calculated this term from correlated wave functions [SDQ-MBPT (4)] using both ab initio MODPOT and the larger all-electron basis sets). From values of the first-order electrostatic multipolar term from SCF and correlated monomer wave functions, the contribution to intermolecular interaction energy due to the use of correlated monomer wave functions has been estimated. Our results indicate either the dominant role of electrostatic term or near cancellation of the remaining components of intermolecular interaction energy. For cyclic nitromethane dimer at equilibrium distance these effects approach 0.9 kcal/mol (nearly 1/4 of total interaction energy). In addition, we showed that the semitheoretical expression and parameters we use for estimating the dispersion energy gave results very close to the published variation perturbation results from the larger basis set calculation.