Calculated atomic volumes of the actinide metals

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Calculated atomic volumes of the actinide metals

H. Skriver, O. Andersen, B. Johansson

To cite this version:

H. Skriver, O. Andersen, B. Johansson. Calculated atomic volumes of the actinide metals. Journal de

Physique Colloques, 1979, 40 (C4), pp.C4-130-C4-130. �10.1051/jphyscol:1979439�. �jpa-00218835�

JOURNAL DE PHYSIQUE Colloque C4, supplément au n" 4, Tome 40, avril 1979, page C4-130

Calculated atomic volumes of the actinide metals

H . S k r i v e r , O . K . A n d e r s e n (*) a n d B . J o h a n s s o n (**)

(*) Department of Electrophysics, Technical University, Lyngby, Denmark (**) Department of Physics, FOA 2, Stockholm, Sweden

Résumé. — On a calculé les volumes atomiques d'équilibre pour les métaux d'actinides. On trouve qu'il est possible de rendre compte, pour l'américium, de la localisation des électrons 5f.

Abstract. — The equilibrium atomic volume is calculated for the actinide metals. It is possible to account for the localization of the 5f electrons taking place in americium.

I n r e c e n t y e a r s it h a s b e c o m e clear t h a t a n u m b e r of g r o u n d s t a t e p r o p e r t i e s of solids c a n b e d e s c r i b e d a c c u r a t e l y using a one-electron picture.

Starting f r o m this r e d u c t i o n of t h e original e q u a - t i o n s , further simplifications c a n b e i n t r o d u c e d t o r e d u c e t h e c o m p u t i n g time [1]. T h u s , e.g. t h e s o - called a t o m i c s p h e r e a p p r o x i m a t i o n ( A S A ) c o m - b i n e d w i t h t h e local d e n s i t y f o r m a l i s m [1] h a s b e e n successfully applied t o c a l c u l a t e v a r i o u s b u l k p r o - p e r t i e s of t h e transition m e t a l s .

Fig. 1. — Comparison between the experimental and the calcu- lated atomic Wigner-Seitz radius, J?Ws, for the actinide metals.

The dashed line corresponds to an estimated value for Ac derived by Zachariasen (Ref. [2]).

I n t h e p r e s e n t c o m m u n i c a t i o n w e apply t h e A S A - m e t h o d t o t h e actinide m e t a l s . F o r t h e lighter ele- m e n t s with relatively b r o a d f - b a n d s , t h e calculated a t o m i c v o l u m e s agree v e r y well with e x p e r i m e n t s (Fig. 1). A t equilibrium conditions t h e f-electrons p l a y t h e d o m i n a n t role in t h e binding for t h e m e t a l s P a - P u . I n n e p t u n i u m a n d p l u t o n i u m s o m e d e v i a t i o n s b e t w e e n t h e o r y a n d e x p e r i m e n t (Fig. 1) a r e f o u n d , w h i c h , h o w e v e r , c a n b e related t o t h e fairly n a r r o w 5f-band for t h e s e t w o m e t a l s . T h u s this indicates t h a t correlation effects b e y o n d t h e p r e s e n t l y e m - p l o y e d one-particle p i c t u r e a r e of i m p o r t a n c e . B y allowing for spin-polarization of t h e metallic f-band, o u r calculations s h o w t h a t for n o n e of t h e earlier metals (=£ P u ) is m a g n e t i s m f a v o u r e d . I t is only w h e n w e apply t h e s c h e m e t o a m e r i c i u m t h a t a stable spin-polarized s t a t e is f o u n d . I n fact t h e f-state in a m e r i c i u m is f o u n d t o b e fully polarized w i t h a n f-occupation n u m b e r of a p p r o x i m a t e l y 6 e l e c t r o n s . T h i s polarized solution t h u s mimics t h e localized f^-state in a m e r i c i u m a n d t h e c o r r e s - ponding calculated a t o m i c v o l u m e agree quite well w i t h e x p e r i m e n t (Fig. 1).

W e c o n c l u d e t h a t t h e p r e s e n t calculation s h o w s t h a t it is possible t o a c c o u n t for t h e variation of t h e a t o m i c v o l u m e in t h e actinide series a n d also t o a c c o u n t for t h e localization within t h e f-shell w h i c h t a k e s place a s a function of a t o m i c n u m b e r [ 3 , 4 ] . A detailed a c c o u n t of this w o r k will b e given e l s e w h e r e .

References

[1] ANDERSEN, O. K., Phys. Rev. B 12 (1975) 3060 ;

ANDERSEN, O. K. and JEPSEN, O., Physica 91B (1977) 317.

[2] ZACHARIASEN, W. H., J. Inorg. Nucl. Chem. 35 (1973) 3487.

[3] JOHANSSON, B., Phys. Rev. B 11 (1975) 2740.

[4] SKRIVER, H., ANDERSEN, O. K. and JOHANSSON, B., Phys.

Rev. Lett. 41 (1978) 42.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1979439