FÍSICA DA MATÉRIA CONDENSADA - Sociedade Brasileira de Física

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CRI/8:30/4 4 f.
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tvanm P. Rmetarw:hmR - IFOSq
CRI/9:10/4 4 f. ESTRUTURAS MODULADAS BID1EENS10NAIS: UMA SINULACiO
Nivaldo Lucie Special! e Carlos Basilio Pinheiro - Dept ') de Flaice - UFNO
No espectro de Macio de estruturas medulada ■ observars@ um conjunto de
raflexass principais e um conjunto de reflesies satilites. Al primeiras estio relaciona
das cam ■ estrutura de base, predominante no }o cristalino, • as segunda. aio ass;
ciadas e variaçóes periódicas qua ocorria na poslces dos Atemos a/ou na ocupaçio doe
sitie.. A indaxacio dos várias panto. da rede recíproca i feita com 3+d indlesa i.tei
roo h k 11/ 1
t ... md senda d a dimensio da modulacio.
Resolver a estrutura nun caso geral significa encontrar as posicies
dos átomos a a.trutura de base, on deslocamentos rYi e a [unçio de eprobabilidada dm
ocupaçie
No processo de procura e aoluçio da estrutura, a distribuiçio des reflaliss
.atllites die indicaçóes iniciais com respeito is funçóes de modulaçio.
Nós ■ ienlamos estruturam moduladas bldimensionala numa escale tal quo pu
dessem. usar LASER para obter o espectro da difraçio. A dependeneia do aspecto geral
do espectro rem o tipo de modulaçio Mel estudado; aqui apresaeteremoe alguns resultado..
CRI/4:30/4' !. I ON Ili EXPANSION OF RARLE-NAUFTNAN(E-N) DETERMINANTS INTO MULTIPLETS.
By O.E.Piro, My. co Depta.of IFQSC.USP,C.P.369.13.560 Sio Carlo..SP ■ Brasil and UnLv.Nac.
de La Flat.. C.C.67.1900 La Plata. Argentina and C.D. Rango.C.Tsoucari ■ and .1.N . Lab.
de Pbysique.Facuití de Pharmacle.Univ.de Paris-Sud.92290 Chatenap-Nalabry.Pranca.
Improved Direct Method formulations employing besides triplets. quartet and quintet
products of structure factors(phase invarients)elearly suggest the useful phase Information
conveyed by higher-order multipless is structure determination procedures. These
formulations can be obtained from the first few terms in the expansion of large joint
probability distribution(j.p.d.) of structure factors constructed on the basis of Ii-N
determinants. In this connection. it has been pointed out that the power of
Direct Natho= to solve large crystal structures is limited by the usual practice of
approximating large j.p.d.'s by piecing together marginal distributions of single
invariants. It in therefore in ing to describe how the full phasing power of large
j.p.d.'e is reached by the pogressive incorporation of phase information due to higherorder
meltiplets. As a contribution to this goal. we disclose herewith the group
th ical structure of the Muting phase invariants in the expansion of an
arbitrary m-order R-H determinant into mltiplets up to the order m. Implication: and
possible applications of the results will be discussed.
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