Foreword

Foreword

MARTIN KAUPP, VLADIMIR G. MALKIN

agnetic resonance spectroscopy is an indis-M pensable tool in many areas of the naturalsciences, ranging from biology and medicine tomaterials research. In chemistry, nuclear magnetic

Ž .resonance NMR spectroscopy and electron para-Ž .magnetic resonance EPR spectroscopy together

arguably represent the most widely used class ofspectroscopic techniques. It is thus understandablethat the quantum-chemical treatment of magneticresonance parameters has become an importantbranch of theoretical and computational chemistry.However, the history of quantitative calculationsin this area from first principles is not as long asone might think. There are a number of difficulties

Ž .with magnetic vector properties that preventedearly success of quantum-chemical techniques. Anexample is the well-known gauge origin problemŽ .e.g., for NMR chemical shifts . The practical solu-tions using distributed-gauge methods like IGLOand GIAO only started to bear fruit in applicationsin the mid-1980s. At last, chemical shifts could becomputed with reasonable accuracy for systems ofchemically relevant sizes! The progress marked bythese seminal achievements was documented inthe very successful conference on NMR chemicalshifts at the University of Maryland in 1992, orga-nized by Prof. J. A. Tossell.

Since then, the field has been transformedtremendously and may now be considered a ma-ture and substantial subdiscipline of quantumchemistry. Progress has been made on variousfronts: sophisticated post-Hartree]Fock methodshave been developed to account for the effects ofelectron correlation. Density functional methodsŽ .DFT came into play as a more economical alter-native to include correlation in an approximatemanner, applicable to calculations on large

molecules. This also opened the way to systemscontaining transition metals and other heavy ele-ments. As a consequence, relativistic effects had tobe treated, and considerable progress with theinclusion of both spin]free relativistic and spin]orbit effects has been made in the past few yearsand is continuing at present. The conceptually newinsights that have developed are changing thequalitative interpretation of NMR chemical shiftsŽ .and of other NMR and EPR parameters . As theaccuracy of the computed chemical shifts in-creases, additional factors, such as rovibrationaland environmental effects, are being dealt with;both these areas are blossoming. The same is truefor the combination of magnetic resonance param-eter calculations with molecular dynamics simula-tions, which is being used increasingly to obtaindynamical information.

Until recently, chemical shift calculations domi-nated the focus of research and continue to beinvestigated extensively. Among the other NMRparameters, indirect spin]spin coupling constantsare particularly difficult to compute, in part due tothe need for an accurate treatment of electroncorrelation even with light main group systems.Again, the development of post-Hartree]Fockmethods and the use of DFT expanded the limitsof what might be done, and the calculations ofspin]spin coupling constants can be expected tobecome routine during the next decade. Relativis-tic corrections also are being considered increas-ingly, and all the other aspects just mentioned forchemical shifts have been addressed at least pre-liminarily in recent work.

In 1997, in response to the need for a betterexchange between workers in the field, plans foran international conference on the calculations of

( )Journal of Computational Chemistry, Vol. 20, No. 12, v]vii 1999Q 1999 John Wiley & Sons, Inc. CCC 0192-8651 / 99 / 12000v-03

KAUPP AND MALKIN

magnetic properties of molecules took shape. Itwas clear that the ‘‘smaller brother’’ of NMR, EPRspectroscopy, also should be included. EPR hyper-fine coupling constants are similar to NMRspin]spin coupling constants, both formally and interms of computational difficulties. Electronic g-tensors of EPR are related conceptually to NMR

Žchemical shift tensors and on a different level also.to spin]orbit corrections to NMR parameters .

Hence, the symposium held on September 14]18,1998 at the beautiful Smolenice Castle nearBratislava, Slovak Republic, was titled ‘‘Interna-tional Conference on Quantum Chemical Calcula-tions of NMR and EPR Parameters.’’ More than 70scientists from all over the world attended themeeting. The topics ranged widely from methoddevelopment and validation to applications inmany areas of chemistry, biology, and materialsresearch. A number of lectures by experimentalworkers, including the plenary lecture of Nobel

Ž .Laureate Richard R. Ernst Zurich, Switzerland ,¨

underscored the prominent role that quantum-chemical calculations now can play in various ar-eas of magnetic resonance spectroscopy. Manystimulating discussions across subdiscipline bor-ders took place in the pleasant surroundings of thecastle. Ideas were exchanged between method de-velopers and applications experts, between theo-reticians and experimental workers, between spe-cialists in NMR and EPR, and between youngerand older researchers.

This special issue has grown out of the 1998Smolenice Conference, but is not a symposiumproceedings summary in the traditional sense. Wehave not required the contents of the manuscriptsto be identical to those presented at the meeting.Moreover, the 11 articles published in this specialJCC issue are not fully representative of the 4-dayconference which consisted of more than 30 lec-tures and a similar number of posters. Thus, whileseveral of the most important topics are included

Žhere e.g., relativistic and environmental effects on

On the occasion of the NMR EPR-98 conference, Werner Kutzelnigg received the Diony)z Ilkovic Medal of the Slovakˇ( ) ( )Academy of Sciences. From right to left: Drs. Werner Kutzelnigg Bochum , Richard R. Ernst Zurich , Vladimir G. Malkin¨

( ) ( ) ( ) (Bratislava , Olga L. Malkina Bratislava , Martin Kaupp Stuttgart , Ludger Buerstedde German ambassador to the) ( )Slovak Republic , and Stefan Luby President of the Slovak Academy of Sciences . Further photographs from and

information on the program of the conference may be found at: http:// www.theochem.uni-stuttgart.de/ ; mkaupp /smolen.html.

VOL. 20, NO. 122

FOREWORD

NMR and EPR parameters, the calculation andinterpretation of chemical shifts, spin]spin cou-

.pling constants, and hyperfine coupling constants ,other topics are not presented. A prime example iselectronic g-tensors, the quantitative calculation ofwhich has made much progress; several talks bymost of the leading researchers in the fieldprompted considerable discussion throughout theconference.

Nevertheless, we hope that this issue will givethe reader at least an impression of the remarkableprogress that has been made in quantum-chemicalcomputations of magnetic resonance parametersduring the last few years. We expect developmentsto continue in this exciting and important area andlook forward to the follow-up conference, whichhas been tentatively planned for 2001 or 2002 inSweden.

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