Published in:
The Journal of Chemical Physics, 82 (1985) 3, Seite 1413-1419
Language:
English
DOI:
10.1063/1.448464
ISSN:
0021-9606;
1089-7690
Origination:
Footnote:
Description:
The F2 ground state potential curve has been computed near re by means of the MCSCF, CI(SD), MR-CI(SD) and the recently proposed CPF method. Extensive sets of polarization functions including up to five d sets, three f sets, and one g set have been used to study the convergence of the total energy of De, and re for these methods on basis set extension. SCF and MCSCF show a similar behavior and are practically converged on the 2d1f level. Convergence is much slower for methods which include external correlation, such as CI(SD), MR-CI(SD), CPF. The largest calculation performed—MR-CI(SD) for a [6 4 2 1] basis—included 280 076 configuration state functions, and yields De and re with an accuracy of 0.07 eV and 0.015 a.u. These remaining errors are attributed mainly to the neglect of g functions. The present results provide detailed information concerning the relative importance of polarization functions which can be ordered as: d(1)>d(2)≳f(1)>d(3) for SCF and MCSCF and d(1)>f(1)≳d(2)>g(1)≳f(2)≳d(3) for methods including external correlation.