An alternative view of the coherent x-ray scattering factor with application to the hydrogen atom Am.The x-ray form factors for a bonded hydrogen in the hydrogen molecule have been calculated for a spherical approximation to the bonded atom. These factors may be better suited for the least-squares refinement of x-ray diffraction data from organic molecular crystals than those for the isolated hydrogen atom. It has been shown that within the spherical approximation for the bonded hydrogens in H 2 , a least-squares refinement of the atomic positions will result in a bond length (R. value) short of neutron diffraction or spectroscopic values. The spherical atoms are optimally positioned 0.07 A off each proton into the bond. A nonspherical density for the bonded hydrogen atom in the hydrogen molecule has also been defined and the corresponding complex scattering factors have been calculated. The electronic density for the hydrogen molecule in these calculations was based on a modified form of the Kolos-Roothaan wavefunction for H2• Scattering calculations were made tractable by expansion of a plane wave in spheroidal wavefunctions. 5 Compare K. Ruedenberg, Rev. Mod.

AbstractsA contracted Gaussian basis set capable of describing about 63% of the correlation energy of N, has been used in a detailed configuration-interaction calculation. Secondorder perturbation theory overestimated the correlation energy by 23-50 % depending on how H o was chosen. Pair-pair interaction affects the correlation energy by about 20 % while quadruple excitations have an 8 % effect.Un calcul CI dttaillt pour N, a Ctt fait avec une base Gaussienne contractte capable de dtcrire environ 63% de 1'Cnergie de corrClation de cette moltcule. Avec la thtorie des perturbations du second ordre I'tnergie de corrtlation est surestimCe de 23 A 50%, dCpendant du choix de HO. Les interactions paire-paire donnent environ 20 % de 1'Cnergie de corrklation tandis que les excitations quadruples donnent 8 %.Ein zusammengezogener Basissatz von Gaussfunktionen, der ungefahr 63 % der Korrelationsenergie von N, beschreiben kann, ist in einer eingehenden cI-Berechnung verwendet worden. Die Storungstheorie zweiter Ordnung uberschatzt die Korrelationsenergie mit 23-50%; wieviel hangt von der Wahl von H o ab. Die Paar-Paar-Wechselwirkung gibt ungefahr 20 % der Korrelationsenergie und die Kvadruppelanregungen 8 %.

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