Phenomenological and Microscopic Theories of Structure
The NEC Corporation are to be congratulated for their foresight in setting up these biennial symposia on “The Fundamental Approach to New Material Phases”. This is indeed a timely step, for during the past few years a meaningful dialogue has started between fundamental theorists, materials scientists, and engineers who are interested in designing materials (see, for example [l]). This dialogue has arisen partly because quantum theorists are now beginning to predict from first principles the cohesion and relative structural stability of equilibrium and metastable phases. The advent of fast computers and the development of efficient computer codes have demonstrated that the intuitive and very simple Hartree-type equations of the Local Density Functional (LDF) approximation  are usually sufficient  to calculate the ground state properties of molecules and solids within a few percent (see, for example, , , and ). The present symposium has numerous papers which assess the accuracy of the LDF approximation in predicting the properties of microclusters.
KeywordsMagnesium Tate Boride Beryllium CsCl
Unable to display preview. Download preview PDF.
- 1.High Temperature Alloys: Theory and Design, ed. by J. 0. Stiegler, Bethesda Conference Proceedings (The Metallurgical Soc. of AIME, Warrendale 1984).Google Scholar
- 3.Non-locality of exchange and correlation can sometimes be important as, for example, in Be2 .Google Scholar
- 7.W. B. Pearson: The Crystal Chemistry and Physics of Metals and Alloys (Wiley, New York 1972).Google Scholar
- 9.The quantum mechanical pseudopotential radii used by Villars in  essentially measure the size of the free atom. This decreases monotonically across a given period unlike the bulk atomic volume which is determined by competition between the size of the free atom and the strength of its bonding to its neighbours (see §6 of D. G. Pettifor: in Sol. St. Phys, ed. by H. Ehrenreich and D. Turnbull, (Ac. Press, Florida, to be published, Spring 1987)).Google Scholar
- 11.D. G. Pettifor, New Scientist 110, No. 1510, 48 (1986). Note that there are some differences in the relative ordering of the 4d and 5d transition elements provided by the string compared to the earlier table 1 of . This does not affect the structural separation. The string values for the Mendeleev-number will be used consistently in future.Google Scholar
- 12.Other authors such as A. Zunger in Phys. Rev. Lett. 47, 1086 (1981). and P. Villars and K. Girgis in Z. Metallk. 73, 445 (1982) have used the periodic table to present in matrix form structural or other empirical data. However, Zunger and Villars were both discouraged by the poor structural separation they obtained so that they favoured the use of physical co-ordinates in their search for structural ordering. The way the string runs through the periodic table is of crucial importance for successful structural separation; as too is the realization that two-dimensional ordering of all the data for a given stoichiometry can only be achieved with a single phenomenological co-ordinate.Google Scholar
- 16.R. C. Evans: An Introduction to Crystal Chemistry, 2nd ed. (C.U.P., Cambridge, 1966).Google Scholar
- 17.W. M. C. Foulkes: (to be published).Google Scholar
- 18.M. W. Finnis, D. G. Pettifor, A. P. Sutton, and Y. Ohta (to be published).Google Scholar
- 23.J. Majewski and P. Vogl: Phys. Rev. Lett, (to be published).Google Scholar