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In a series of papers we investigate the localized orbital contributions at the molecular experimental and theoretical equilibrium geometries using various basis sets. The present study deals with some energy quantities obtained from loealized charge densities: the kinetie, the (effective) potential and the selfinteraction energies ate discussed. Several regula¡ were found for the systems considered, namely the molecules HF, H~O, NH 3 and CH4, respeetively. IntroduetionAs the simplest a n t i s y m m e t r i c w a v e f u n e t i o n of a closed-shell system, a single d e t e r m i n a n t of one-particle functions is i n v a r i a n t under a n y u n i t a r y transformation [1], the t r a n f o r m a t i o n s could be chosen to o b t a i n new orbitals localized as m u c h a s possible [2]. Several localization procedures have been published as well as m a n y a d v a n t a g e s of using localized orbitals have been pointed out recently [3--7]. In a series of papers we also investigated various properties of localized charge densities for some ten-a n d eighteen-eleetron systems [8--11].I t is k n o w n t h a t in a n y q u a n t u m -c h e m i c a l calculation the p r o b l e m arises whieh t y p e of basis set and which g e o m e t r y d a t a ate to be used for the study of the given molecular system. As to the choice of a suitable basis set, there are usually the c o m p u t e r time and/or size which m a k e a limit for the n u m b e r of basis functions. I t has been pointed out, e.g., t h a t at least one d function on the oxygen is necessary to take for the molecule H~O in order to obtain an acceptable value for the total energy as well as for the electrie m o m e n t s (more details on basis set dependence see in [12--14]). Ah exhaustive analysis of the effect of basis set v a r i a t i o n on the localized charge distribution of H~O has also been done [1]. F r o m the results it follows t h a t in the presence of polarization functions (at least one d-type on the oxygen) the energy contributions as well as the eleet¡ m o m e n t c o m p o n e n t s provide regular differences for b o n d and lone pair loealized orbitaIs. The change of energy c o n t ¡ parallels with t h a t of total energy and similarly the first and second order m o m e n t components (localized moments) with t h a t of the corresponding total molecular Acta Physiea zicaderniae Scientiarum Hungarir 46, 1979

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