Richard M. Fye

We write in memory of our wonderful friend and colleague, Richard M. Fye. He was born on 7 February 1956 and left us on 10 September 2023.

Richard received his PhD in 1988 from the University of California, San Diego (UCSD). As a graduate student, with his adviser Jorge Hirsch, he made a number of significant contributions to computational physics, particularly in modeling systems of correlated electrons. Together they developed the Hirsch–Fye algorithm, a well-controlled quantum Monte Carlo approach that they used to study small clusters of magnetic impurities in metals, also in collaboration with Hai-Qing Lin, a UCSD graduate student at the time. Then Richard went on to apply the method to study classic heavy-fermion-related problems, the 1D Anderson and Kondo lattices. Numerous investigators have since used the Hirsch–Fye algorithm to understand the effect of magnetic impurities on superconductors, negative-U and Holstein impurities, quadrupole impurities, and more.

The Hirsch–Fye algorithm also achieved great prominence as one of the earliest and most powerful “impurity solvers” in dynamical mean-field theory, and its combination with electronic structure methods (LDA+DMFT). In that context, the Hirsch–Fye method has deepened the understanding of high-temperature superconductivity and heavy-fermion systems.

As a graduate student, Richard also derived the leading error term for the so-called Trotter, or short-time, approximation, which underlies virtually all quantum Monte Carlo, as well as deriving and showing how to improve various anomalies of this approximation. As with his other work, he laid the groundwork for broad areas of computational physics: “Trotterization” is now a key methodology in the study of the time evolution of qubits, e.g., in quantum computers.

Richard joined Doug Scalapino’s group in Santa Barbara as a postdoc in 1988 and continued making important contributions to correlated electron physics by himself and in collaboration with Richard Scalettar, Scalapino, and others. He then accepted a permanent appointment in 1991 at Sandia National Laboratories, where he continued to work on strongly correlated materials and on the development of new numerical methods for simulating DNA strand separation. Not long after joining Sandia, his health was compromised by a serious illness, diminishing his ability to fulfill the great promise of the path on which he started. Nevertheless, Richard’s profound achievements led to him being selected in 2006 as a fellow of the American Physical Society.

Besides his impact on computational physics, Richard was a kind soul and a good friend. Before he became ill, he was a devoted and talented long distance runner. He was always jotting down the millions of phrases, poem ideas, scientific and mathematical mysteries, cartoons, and “stuff” running through his remarkable brain in notebook after notebook.

Rick loved his animal companions, from Hammiey the hamster (he couldn’t have a conventional name!), to Spooky the poodle, to Spoofy the poodle, to Rick’s beloved cats: Shatzi, Princess Tapioca, Hermione, and Buddy.

Richard can be remembered at this memorial website .

He will be greatly missed.

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