Alfonso Baldereschi

With profound sadness we have learned that our colleague, collaborator, and friend Alfonso Baldereschi passed away on 22 April 2024 in Trieste, Italy. He was an emeritus professor of physics both at the Federal Institute of Technology (EPFL) in Lausanne, Switzerland, and at the University of Trieste.

After his studies at the University of Milan and the prestigious Scuola Normale Superiore in Pisa (Italy), where he was largely recognized as the brightest student of Franco Bassani ‘s influential school, Alfonso moved to the US. There, he was first a research associate at the University of Illinois Urbana (1969). Soon after (1971), Alfonso was appointed as a technical staff member at the Bell Laboratories, New Jersey, one of the most prestigious research centers in the world: a stellar career path.

He soon became well-known worldwide for his proposal (1972) that the calculation of physical quantities such as the electron density, requiring averaging over the Brillouin zone, could be reduced to the value at a special single k-point. He named it the mean value point, but since the very beginning it has been known as the Baldereschi point. In the early 1970s, computer capabilities were extremely limited. By rendering the calculation of the electron density affordable, the Baldereschi point technique (later extended by others) opened up the possibility not only of representing the distribution of the charge density of real materials, but also of self-consistent iterative evaluations.

Due to family reasons, in 1973 Alfonso had to return to Europe and settled down in Lausanne, where the EPFL had recently been established (1969). There, Alfonso pioneered what we now call computational materials science, based on advanced theoretical methods and the knowledge of the electronic structure. His reputation was instrumental in rendering the EPFL a major center on the map of condensed-matter-physics research. In particular, his presence soon started to attract many researchers to either join or visit the EPFL. Already in 1978, the International Conference on the Physics of Semiconductors was known by many as the Baldereschi conference.

Over the years, a large group of collaborators shared the privilege of working with him, benefiting from his vast and deep knowledge, and also from his generosity and amiability.

In 1981 he accepted the chair of structure of matter at the University of Trieste, while still continuing to teach at the bachelor, master’s, and PhD levels at the EPFL in Lausanne. There, he held the chair of computational physics and also served periods as director of the Institute of Theoretical Physics and of the physics department.

Alfonso was steadily engaged in supporting any initiative for the diffusion of computational condensed-matter research. In particular, he founded (and directed at various stages) the Institute for Computational Materials Science (IRRMA), which fostered unprecedented collaborations among the EPFL and the Universities of Geneva, Neuchâtel, and Fribourg.

Alfonso’s research was devoted both to the development of elegant computational methods and to diverse important applications. His special focus was on the electronic, optical, and dielectric properties of materials such as (elemental and compound) semiconductors and amorphous silica, thus unraveling the effects of impurities as well as of compositional and structural disorder. But his scientific span went way beyond that, including, for example, catalysis.

Alfonso and early collaborators developed the first comprehensive approach to impurity as well as exciton levels in semiconductors, with predictive results in agreement with experiments. He pioneered the quantitative calculation of band offsets at semiconductor interfaces, of piezoelectric and ferroelectric polarization, and of surface physico-chemical processes from first principles. He discovered the interlayer states, of great importance to 2D materials like graphite and graphene, as well as 1D materials like polyethylene. He carried out the first quantitative calculations of nonlocal dielectric screening in crystals. And much more. A special feature of Alfonso’s papers was to accompany the presentation of complex and accurate calculations with either a simpler scheme that captured the fundamental physics or a model that explained the results more clearly. That transformation of a physical mechanism from specific to universal is the hallmark of great masters.

Alfonso’s personality, his human side, and his sense of humor were, as everything else, also special. His discussions and lectures, from his student times in Pisa, were as enthralling in their content as they were undetermined in time and duration. Simply, every aspect had to be unraveled inside and out to satisfaction, never mind how long it took.

Alfonso has been recognized by generations of students as an absolutely unique teacher: crystal clear in his explanations, stimulating, enthusiastic, and charismatic. Indeed, he brought to teaching the same devotion, passion, and unmitigated honesty that he did to research.

Alfonso’s outstanding contributions to science, the physics schools he created in Lausanne and Trieste, stand as landmarks in our field. All that, coupled with his generosity and great kindness to all his colleagues, collaborators, and students will never be forgotten.

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