Lisp-Stat to Java to R

This paper will describe my experiences in moving on from Lisp-Stat to Java to R. I was introduced to Lisp-Stat in'89 and used it actively for teaching and research over the next 10 years. My use of Lisp-Stat culminated in a joint project with Hani Doss on Bayesian Sensitivity Analysis and it remains the largest piece of software I wrote using Lisp-Stat. At the time the project was completed, the only open statistical system that could deliver the goods was Lisp-Stat. In this article, I will describe how the power of Lisp, underlying statistical components and dynamic graphics were exploited in the project. When development on Lisp-Stat slowed down, Java was coming into its own as an important language and R became an open source collaborative project. Of course, I have moved on and I use R for most of my work today. I will touch upon my experience with Java and R briefly.

A Model for the Thermal Expansion of Ag(111) and other Metal Surfaces

We develop a model to study the thermal expansion of surfaces, wherein phonon frequencies are obtained from ab initio total energy calculations. Anharmonic effects are treated exactly in the direction normal to the surface, and within a quasiharmonic approximation in the plane of the surface. We apply this model to the Ag(111) and Al(111) surfaces, and find that our calculations reproduce the experimental observation of a large and anomalous increase in the surface thermal expansion of Ag(111) at high temperatures [P. Statiris, H.C. Lu and T. Gustafsson, Phys. Rev. Lett. 72, 3574 (1994)]. Surprisingly, we find that this increase can be attributed to a rapid softening of the in-plane phonon frequencies, rather than due to the anharmonicity of the out-of-plane surface phonon modes. This provides evidence for a new mechanism for the enhancement of surface anharmonicity. A comparison with Al(111) shows that the two surfaces behave quite differently, with no evidence for such anomalous behavior on Al(111).Comment: 17 pages, 4 figures, to appear in Z. Chem. Phy