Showing papers by "Enrico Clementi published in 1990"

A comparative study of density functional models to estimate molecular atomization energies

Abstract: In the present study the molecular atomization energies have been computed with some of the recent density functionals and with a semiempirical model developed in the IBM laboratory. In particular, the Lie–Clementi (LC), the Colle–Salvetti (CS), the Gunnarson–Lundqvist (GL), the Vosko, Wilk, and Nusair (VWN), the Perdew–Zunger (PZ), the Becke (B), and the Lee, Yang, and Parr (LYP) functionals have been considered. For GL and VWN the self‐interaction correction of Stoll, Pavlidou, and Preuss (SPP) has been included. For the PZ the gradient correction of Perdew has been included. For the LYP a new and simpler form as proposed by Michlich et al. has been implemented. More than 50 small to fairly large molecules have been chosen at test cases. The results obtained with the present semiempirical model are gratifying and indicate that further improvement and calibration is still possible. From the computed data it is concluded that the density functionals in most cases do provide a pragmatic solution to the det...

Gaussian functions in Hylleraas‐configuration interaction calculations. V. An accurate ab initio H+3 potential‐energy surface

Abstract: The near‐equilibrium potential‐energy surface of the 1A’1 ground state of H+3 has been calculated at 69 different points with the Hylleraas‐configuration interaction method using 13s3p1d Cartesian Gaussian basis functions. This new surface is found to be substantially lower in absolute energy than all previous surface calculations. The equilibrium energy of the H+3 molecule has also been calculated with a larger 13s5p3d basis set. The minimum energy was found to be E=−1.343 827 9 hartrees at an internuclear distance of R=1.6500 bohrs in the equilateral triangle configuration. This energy is significantly (>70 cm−1) lower than the previous best published variational calculation and is outside and below the error bars of the latest quantum Monte Carlo calculation. In addition, a medium‐sized basis set of 13s4p2d orbitals was used to predict that the equilibrium separation is R=1.6499 bohrs.

Gaussian functions in Hylleraas‐configuration interaction calculations: Potential curves for the e 3∑+u and the f 3∑+u states of hydrogen

Abstract: The explicitly correlated wave function method (Hylleraas‐CI) with Cartesian Gaussian basis sets has been used to calculate the potential curve for the e3∑+u and f 3∑+u states of the H2 molecule. Potential barriers of 215 and 10 300 cm−1 are predicted to exist in the e3∑+u and f 3∑+u states, respectively, and their nature analyzed. Spectroscopic constants for H2 and D2 derived from the curves are compared with experiments and other theoretical calculations. It is concluded that the present potential curves are the best theoretical ones to‐date and their accuracy is probably as good as the scanty experimental data. No o3∑+u state below the f 3∑+u state is found in our calculations.