H. Oyanagi , ETL, Japan

It is strongly needed to establish a centralized center for theoretical studies on several areas where interdisciplinary efforts are expected to boost the development beyond the present limitations. This is because in certain research areas, not only specializing efforts but also generalizing, or in some cases, interdisciplinary efforts are strongly needed. In most cases, potential users will be greatly benefited.

There are two aspects for the direction which we should take; the systematic correlated or collaborated development of fundamental theories which is expected to provide the understanding, and the development of codes which, based on these theoretical backgrounds, will provide access to all potential researchers in a related field.

The former approach has been practiced independently by universities and institutes but it should be stressed that we now need a global collabotation to achieve a breakthrough among researchers since the remaining problems are well focused and need a systematic investigations, with a proper arrangement.

Further, in order to develop a practical tool, the development of a standard tool can be done only by a special team in collaboration with theory group.

These approaches are expected to provide oppotunities of breakthrough in basic theory and a global standard in codes. Such a role can be played by a centralized theory center backed up by a computational facility. Although computing facilities are not necessarily at the same place, it is very important that at this center, theoreticians work in collaboration with programmers.

I recomend to set the taget of the second category, i.e., development of a practical tool as a global standardpackage. It consists of modules having independent functions and if needed, these functions are combined.

If we take photoelectron phenomena as an example, the package allows us to build a target crystal (surface) in a computer, then one can view 3D structure and obtain pair distribution functions around a specified atom. One can also simulate diffraction patterns for powder, spot and CTR etc. and calculate PD pattern and its initial energy dependence (angle-resolved Photoelectron Fine Structure), angle-integrated Photoelectron Fine Structure (nearly EXAFS), EXAFS and XANES as a function of polarization. None of the previous codes have these capabilities although potential users are forced to work independently on these issues.

A centralized theory center can implement such a global standard tool if it is formed as proposed.

As an example, let us focus on angle-resolved Photoelectron Fine Structure (ARPFS). Its theoretical backgrounds date back to 1970's. Recently a new detector became available, which can provide angular distribution of a particular photoelectron peak simultaneously. If the 2D distribution is measured as a function of the initial excitation energy, 3D (vast memory size) is easily obtained. However, the analysis of such a 3D map needs a special code which has never been achieved. With the aid of high performance computer, it is now possible to handle enormous quantity of data.

In conclusion, a theory center concept is welcomeed as a global standard which should be implemented in early 2000.