Abstract
The interpretation of atomic observations by theory and the testing of computational predictions by experiment are interactive processes. It is necessary to gain experience with “the other side” before claims of achievement can be validated and judged. The discussion covers some general problems in the field as well as many specific examples, mostly organized by isoelectronic sequence, of what level of accuracy recently has been reached or which atomic structure or level lifetime problem needs more attention.
Highlights
Let me refer to higher authority for guidance in the task prescribed in the title
With increasing nuclear charge Z, there increases the probability of a spin-changing decay branch of the 2p2 1D2 level to the 2s2p 3Po1,2 levels. (A corresponding case, the 3p2 1D2 level decay, with in-system and intercombination decay channels, occurs in the Mg isoelectronic sequence [32,133].) One might expect that any atomic structure code operating in intermediate coupling would include this decay branch automatically, but the scarcity of literature data and the scatter of the results of the few available computations tell a different story
I know of Livermore colleagues who encountered at least one referee who wanted to discourage them from applying more experiments to this very problem, since—in the strongly expressed view of the referee—a theoretician had finished off the problem for good—and anyway the National Institute of Standards and Technology (NIST) electron beam ion traps (EBIT) experimental results agreed with that material
Summary
Let me refer to higher authority for guidance in the task prescribed in the title. Burkhard Fricke, Professor of Theoretical Physics at Kassel, some time vice president of his university, recalls advice by his elders as “If theory and experiment disagree, work on theory; if they agree, improve the experiment.” Alan Hibbert, professor in the Department of Applied Mathematics and Theoretical Physics at Queens University Belfast and sometime Dean of the Faculty of Theology, would add a caution to this: “If theory and experiment agree, be aware of the possibility that both may be wrong.” Right. My aim in this article is a discussion of what I as an experimenter expect from theory and atomic structure computations, how I try to assess the quality of the work, and what experiment can or can’t do towards a critical validation process of such calculations. There is the Ritz variation principle that states how any imperfection in the wave function of the lowest state of a given symmetry will result in a calculated energy higher than in nature/truth For decades this insight has fired a competition for reaching a lower value for the computed energy of the ground state of the He atom, and the guidance has resulted in excellent achievements. It should come as no surprise that not all of them have been solved yet It takes comparisons between nature/experiment and theory/computation to find out about the amount of detail that needs to be explored. In many cases the comparison of computation and measurement will point out a need of further debugging the codes and/or to better experiments
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