Werner Eissner (1930–2022): A Pioneer in Computational Atomic Physics
Professor Mike J. Seaton was planning a grand project in atomic physics. Space research was expected to soon provide astrophysics with a plethora of UV-spectra coming from the most varied objects such as the solar corona, AGNs, and planetary nebulae, originating from medium and highly ionised atoms. To identify and interpret these spectra, the atomic data were mostly missing. A computer should construct the atomic structure along the lines of Condon and Shortley, and no longer be performed by hand with Clebsch–Gordan coefficients adding stepwise one-electron functions to arrive at the desired n-electron atom. I remember that, on a visit late in 1966, Mike Seaton told me about his plans and offered me a position on the project. The European Space Research Organisation (ESRO) provided the required grant. Mike also told me that a grant had already been found for Werner Eissner. Early in 1967, the group was formed with four members: John Belling, Werner Eissner, John Tully, and me. In a long session, Seaton explained the task. We should organise the way we felt best. He would always be available for advice but did not want to be involved in details. However, as Belling and Tully were also involved in other tasks, the atomic structure group was soon reduced to Eissner and me.
Once it was clear what the computer program should and might be able to do, we split the work. Werner developed the algebraic structure and I the radial functions. I was also supposed to look at the astrophysically required data. The programming was not a straightforward thing. We soon hit storage problems, and a lot of work went into the organisation of the overlay structure. To economise computer time, Werner’s flair for finding clever solutions for the algebraic problems was exceedingly helpful. As our first aim was highly ionised systems, we initially thought that a potential might serve for constructing the radial functions. However, after a few trials and in the view of the long-term aim of having a truly general program, we chose a modified Thomas–Fermi potential. There were plenty of occasions when we consulted Mike: his advice was invaluable.
Werner was a very gentle, lively, and interesting person. We had many discussions over and after coffee, particularly on history. What initially complicated our collaboration was his quest for perfection. Looking for a solution was always fun, but agreeing when the solution was good enough was another matter. However, we soon developed a mutual feeling for the right moment of mutual consent.
We finished structure and published it in 1969. Werner and I wanted Mike Seaton to be a co-author, but he very generously refused. We acknowledged his contribution with: “The advice of Professor M.J. Seaton at every stage of this work was of great help”. Werner then went full speed to develop his collision program. Werner was a godsend for Mike Seaton’s atomic data project. For Werner, the project was a godsend as well, he loved it and dedicated all his energies to it.
In 1974, I met Werner while spending a few days at University College London learning how to use the superstructure and Distorted Wave codes. Having performed most of the coding, he was an expert in both of them. I acquired these programs, but I did not learn enough. I needed a lot of help not only in the beginning but for many years into the future. With the help of a systems engineer, we sometimes had three-way discussions on the telephone about adapting these codes. Werner visited me at the Goddard Space Flight Center many times and helped me a lot. Without his help, I would not have progressed much. He stayed at my house, and he was so familiar with my place that while entering the house he would say, “I know where I am going to sleep”. He was always very active. If he was not helping with the codes, he would try to find something to do around the house. Once I was in Belfast having a gathering on a very cold evening; while returning home, Werner found that his bicycle lamp had been stolen, but he managed to travel home on that cold and dark night. He was always determined to do whatever was needed. I will always miss his sage advice.
Funding
Acknowledgments
Conflicts of Interest
Abbreviations
AGN | Active galactic nucleus |
CCP | Collaborative Computational Project |
DL | Daresbury Laboratory |
ESRO | European Space Research Organization |
FRS | Fellow of the Royal Society |
GSFC | Goddard Space Flight Center |
ICPEAC | International Conference on the Physics of Electronic and Atomic Collisions |
NASA | National Aeronautics and Space Administration |
PhD | Doctor of Philosophy |
SST | superstructure |
QUB | Queen’s University Belfast |
UCL | University College London |
References
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Bhatia, A.K.; Lynas-Gray, A.E.; Mendoza, C.; Nahar, S.; Nussbaumer, H.; Pradhan, A.K.; Seaton, A.M.; Wunner, G.; Zeippen, C.J. Werner Eissner (1930–2022): A Pioneer in Computational Atomic Physics. Atoms 2023, 11, 59. https://doi.org/10.3390/atoms11030059
Bhatia AK, Lynas-Gray AE, Mendoza C, Nahar S, Nussbaumer H, Pradhan AK, Seaton AM, Wunner G, Zeippen CJ. Werner Eissner (1930–2022): A Pioneer in Computational Atomic Physics. Atoms. 2023; 11(3):59. https://doi.org/10.3390/atoms11030059
Chicago/Turabian StyleBhatia, Anand K., Anthony E. Lynas-Gray, Claudio Mendoza, Sultana Nahar, Harry Nussbaumer, Anil K. Pradhan, Anthony M. Seaton, Günter Wunner, and Claude J. Zeippen. 2023. "Werner Eissner (1930–2022): A Pioneer in Computational Atomic Physics" Atoms 11, no. 3: 59. https://doi.org/10.3390/atoms11030059
APA StyleBhatia, A. K., Lynas-Gray, A. E., Mendoza, C., Nahar, S., Nussbaumer, H., Pradhan, A. K., Seaton, A. M., Wunner, G., & Zeippen, C. J. (2023). Werner Eissner (1930–2022): A Pioneer in Computational Atomic Physics. Atoms, 11(3), 59. https://doi.org/10.3390/atoms11030059