# Lars Hedin

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{{Short description|Swedish physicist (1930–2002)}}
{{Use dmy dates|date=December 2024}}
{{Infobox scientist
| birth_name        = Lars Tore Hedin
| birth_date        = {{Birth date|df=yes|1930|2|4}}
| birth_place       = [Örebro](/source/%C3%96rebro), [Sweden](/source/Sweden)
| death_date        = {{Death year and age|2002|1930}}
| fields            = [Condensed matter physics](/source/Condensed_matter_physics)
| workplaces        = [Linköping University](/source/Link%C3%B6ping_University)<br>[Lund University](/source/Lund_University)<br>[Max Planck Institute for Solid State Research](/source/Max_Planck_Institute_for_Solid_State_Research)
| alma_mater        = [KTH Royal Institute of Technology](/source/KTH_Royal_Institute_of_Technology)<br>[Uppsala University](/source/Uppsala_University)<br>[Chalmers University of Technology](/source/Chalmers_University_of_Technology)
| thesis_title      = Application of Many-Body Theory to the One-Electron Problem of Atoms, Molecules and Solids
| thesis_year       = 1965
| children = 3
| doctoral_advisor  = {{Ill|Stig Lundqvist|sv|Stig Lundqvist (fysiker)}}
| known_for         = [''GW'' approximation](/source/GW_approximation)<br>Hedin equations
}}
'''Lars Tore Hedin''' (February 4, 1930 – 2002) was a Swedish physicist working on [condensed matter physics](/source/condensed_matter_physics) and [emeritus](/source/emeritus) professor of [Lund University](/source/Lund_University). He is known for the development of [''GW'' approximation](/source/GW_approximation) based on the Hedin equations, named after him.<ref name=":0">{{Cite journal |last=Rehr |first=J J |date=2005-01-01 |title=Lars Hedin and the quest for a theory of excited states |url=https://iopscience.iop.org/article/10.1088/0031-8949/2005/T115/001 |journal=Physica Scripta |volume=T115 |pages=19–23 |doi=10.1088/0031-8949/2005/T115/001 |issn=0031-8949|url-access=subscription }}</ref>

== Life ==
Lars Tore Hedin was born in [Örebro](/source/%C3%96rebro), [Sweden](/source/Sweden) in 1930, son of engineers.<ref name=":1">{{Cite book |last1=Almbladh |first1=Carl-Olof |url=https://www.lunduniversity.lu.se/lup/publication/a8c8c161-345f-4762-bcc1-725bfd8c6353 |title=Physics in Lund - in time and space |last2=von Barth |first2=Ulf |publisher=Lund University, Department of Physics |year=2016 |editor-last=Forkman |editor-first=Bengt |pages=246–261 |translator-last=Sheppard |translator-first=Helen |chapter=Lars Hedin and the theory of solid state physics |editor-last2=Holmin Verdozzi |editor-first2=Kristina |chapter-url=http://history.fysik.lu.se/images/FysicumsHistoriaBok_pdf/EN_PhysicsInLund_web/EN_Bok_14aLHftt_web.pdf}}</ref><ref name=":4">{{Cite book |last1=Schattke |first1=Wolfgang |url=https://books.google.com/books?id=DvlCOjXJF2AC |title=Solid-State Photoemission and Related Methods: Theory and Experiment |last2=Hove |first2=Michel A. Van |date=2003-11-21 |publisher=John Wiley & Sons |isbn=978-3-527-40334-9 |page=VII |language=en |chapter=In memoriam Lars Hedin (1930–2002)}}</ref>

He studied undergraduate physics in [KTH Royal Institute of Technology](/source/KTH_Royal_Institute_of_Technology), obtaining a master's degree in 1955.<ref name=":1" /> He continued to work there writing a licenciate dissertation in 1960 on the elastic properties of crystals in 1960, advised by Lamek Hultén.<ref name=":1" />

In 1960, he entered [Uppsala University](/source/Uppsala_University) for his graduate studies,<ref name=":1" /> working in the group of [Per-Olov Löwdin](/source/Per-Olov_L%C3%B6wdin).<ref name=":0" /> There he became the PhD student of {{Ill|Stig Lundqvist|sv|Stig Lundqvist (fysiker)}} working on many-body theory applied to condensed matter.<ref name=":0" /><ref name=":1" /> Hedin earned a grant to work at [Argonne National Laboratory](/source/Argonne_National_Laboratory) in the United States between 1962 and 1964, going back to Sweden's [Chalmers University of Technology](/source/Chalmers_University_of_Technology) afterwards, where Lundqvist had been awarded a professorship.<ref name=":1" /> Based on his work at Argonne, he wrote his thesis titled "Application of Many-Body Theory to the One-Electron Problem of Atoms, Molecules and Solids" on 30 October 1965.<ref name=":1" /> Hedin had developed a model in 1965<ref>{{Cite journal |last=Hedin |first=Lars |date=1965 |title=New Method for Calculating the One-Particle Green's Function with Application to the Electron-Gas Problem |url=https://journals.aps.org/pr/abstract/10.1103/PhysRev.139.A796 |journal=Physical Review |volume=139 |issue=3A |pages=A796–A823 |doi=10.1103/PhysRev.139.A796|bibcode=1965PhRv..139..796H }}</ref> which later became known as the ''GW'' approximation, where ''G'' is the many-body [Green's function](/source/Green's_function_(many-body_theory)) and ''W'' the screened interaction term.<ref name=":0" /><ref name=":2">{{Cite journal |last1=Aryasetiawan |first1=F |last2=Gunnarsson |first2=O |date=1998-03-01 |title=The GW method |url=https://iopscience.iop.org/article/10.1088/0034-4885/61/3/002 |journal=Reports on Progress in Physics |volume=61 |issue=3 |pages=237–312 |doi=10.1088/0034-4885/61/3/002 |arxiv=cond-mat/9712013 |issn=0034-4885}}</ref> The equations that he developed are called the Hedin equations.<ref name=":3">{{Citation |last1=Hedin |first1=Lars |title=Effects of Electron-Electron and Electron-Phonon Interactions on the One-Electron States of Solids |date=1970 |work=Solid State Physics |volume=23 |pages=1–181 |url=https://linkinghub.elsevier.com/retrieve/pii/S0081194708606153 |access-date=2024-12-06 |publisher=Elsevier |language=en |doi=10.1016/s0081-1947(08)60615-3 |isbn=978-0-12-607723-0 |last2=Lundqvist |first2=Stig|url-access=subscription }}</ref> The ''GW'' approximation became a competitor theory for [density functional theory](/source/density_functional_theory), also developed about the same time.<ref name=":3" /> Due to its computational requirements, it was not until the 1980s that real materials were able to be studied using ''GW'' approximation.<ref name=":1" /><ref name=":2" />

Hedin work with Lundqvist at Chalmers, led to their review paper titled "Effects of Electron-electron and Electron-Phonon Interactions on the One-Electron States of Solids"<ref name=":3" /> in 1970 which became the foundation for most of his work.<ref name=":0" /><ref name=":1" /> Their model became known internationally as the 'Swedish electron gas'.<ref>{{Cite book |last1=Scheffler |first1=Matthias |url=https://books.google.com/books?id=Wl_vCAAAQBAJ&dq=%E2%80%9CSwedish+Electron+Gas.%E2%80%9D&pg=PA140 |title=Walter Kohn: Personal Stories and Anecdotes Told by Friends and Collaborators |last2=Weinberger |first2=Peter |date=2011-06-28 |publisher=Springer Science & Business Media |isbn=978-3-642-55609-8 |language=en}}</ref><ref name=":3" /> The same year, Hedin became professor at [Linköping University](/source/Link%C3%B6ping_University), but the year afterward he accepted a professorship at [Lund University](/source/Lund_University) where he stablished his own group.<ref name=":1" /> In 1994, he accepted the four year position of director of the [Max Planck Institute for Solid State Research](/source/Max_Planck_Institute_for_Solid_State_Research) in [Stuttgart](/source/Stuttgart), Germany.<ref name=":1" /> He returned to Lund University as emeritus.<ref name=":4" />

Hedin used his ''GW'' method to study [photoemission](/source/photoemission). He called this theory the 'blue electron theory',<ref name=":0" /><ref name=":1" /> which he explained as
{{Blockquote|text=By a blue electron I understand an electron which to some degree is regarded
as distinguishable from the other electrons in the medium, among which its moves. This is clearly in violation of the Pauli principle, but I will try to explore where this idea can lead.|source=Correlation Effects in Atoms and Solids, paper presented at the Symposium on Frontiers in Condensed Matter Physics in honor of Stig Lundqvist, 1990 (unpublished).}}
Hedin also worked in [X-ray absorption fine structure](/source/X-ray_absorption_fine_structure) (XAFS), introducing the [local density approximation](/source/Local-density_approximation) for the GW self energy.<ref name=":0" />

Hedin was editor of ''[Solid State Communications](/source/Solid_State_Communications)'' from 1971 to 1990.<ref name=":4" />

=== Personal life ===
He married his wife Hillevi in 1953.<ref name=":4" /> They had three daughters.<ref name=":4" />

== References ==
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{{DEFAULTSORT:Hedin, Lars}}
Category:Swedish physicists
Category:1930 births
Category:2002 deaths
Category:Academic staff of Lund University
Category:People from Örebro

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