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SUMMARY:THEOS-MARVEL Seminar - Prof. Thomas Olsen
DTSTART:20260122T140000
DTEND:20260122T150000
DTSTAMP:20261007T084052Z
UID:145e4ef00af02aca20237fb3c8dfaef1c2d0b4fc118c39e132a17814
CATEGORIES:Conferences - Seminars
DESCRIPTION:Prof. Thomas Olsen\nProf. Thomas Olsen\nTechnical University 
 of Denmark (DTU)\, Denmark\n\nMagnetic excitations from first and second 
 principles. Classical vs. Quantum mechanical approaches\nThe Heisenberg m
 odel has proven highly successful in describing the fundamental low energy
  magnetic excitations in a wide range of materials. On the other hand\, su
 ch excitations originate from electronic correlations and are notoriously 
 difficult to describe by explicit first principles methods. Thus\, the mos
 t common computational approach applies a Heisenberg description\, with ex
 change parameters obtained from first principles – typically DFT. Howeve
 r\, whether or not such mapping entails a classical or quantum mechanical 
 Heisenberg model description has remained unclear. It is also not obvious 
 to what extent such  a distinction matters at all. Here\, we show that th
 e distinction is in fact important. First it is shown that the classical a
 pproximations for the Heisenberg model is in general unreliable for thermo
 dynamic properties. In particular\, it leads to severe underestimation of 
 critical temperatures. Second\, we show that first principles evaluation o
 f Heisenberg parameters typically introduces a systematic error if total e
 nergies are mapped to a classical model rather than a quantum one. We exem
 plify the approach by application to a variety of 2D magnetic materials.\n
 \nAbout the speaker\nThomas Olsen received his PhD from the Technical Univ
 ersity of Denmark (DTU) in 2010. After a postdoc in San Sebastián Spain\
 , he was hired as assistant professor at DTU in 2015 and became associate
  professor in 2018 (current position). His career has been devoted to dev
 eloping first principles methods for solid state physics using density fu
 nctional theory and many-body perturbation theory. More recently\, his ma
 in focus has been on first principles description of magnetic order and ma
 gnetic excitations. In particular\, for two-dimensional materials.
LOCATION:MED 2 1124 https://plan.epfl.ch/?room==MED%202%201124
STATUS:CONFIRMED
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