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Author Nikolaev, A.V.; Michel, K.H. doi  openurl
  Title Elusive s-f intrasite interactions and double exchange in solids: ferromagnetic versus nonmagnetic ground state Type A1 Journal article
  Year (down) 2009 Publication Journal of experimental and theoretical physics Abbreviated Journal J Exp Theor Phys+  
  Volume 109 Issue 2 Pages 286-292  
  Keywords A1 Journal article; Condensed Matter Theory (CMT)  
  Abstract From the theory of many-electron states in atoms, we know that there exists a strong Coulomb repulsion, which results in the electronic term structure of atoms and is responsible for Hunds rules. By expanding the Coulomb on-site repulsion into a multipolar series, we derive this interaction and show that it is also present in solids as a correlation effect, which means that the interaction requires a multideterminant version of the Hartree-Fock method. Of particular interest is the case where this interaction couples states of localized ( f) and delocalized ( s) electrons. We show that the interaction is bilinear in the creation/annihilation operators for localized electrons and bilinear in the operators for conduction electrons. To study the coupling, we consider a simple model in the framework of an effective limited configuration interaction method with one localized f-electron and one itinerant s-electron per crystal site. The on-site multipole interaction between the f- and s-electrons is explicitly taken into account. It is shown that depending on the low-lying excitation spectrum imposed by the crystal electric field, the model can lead not only to ferromagnetism but also to a nonmagnetic state. The model is relevant for solids with localized and itinerant electron states.  
  Address  
  Corporate Author Thesis  
  Publisher Place of Publication Woodbury, N.Y. Editor  
  Language Wos 000270506500014 Publication Date 2009-09-18  
  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 1063-7761;1090-6509; ISBN Additional Links UA library record; WoS full record; WoS citing articles  
  Impact Factor 1.196 Times cited 3 Open Access  
  Notes Approved Most recent IF: 1.196; 2009 IF: 0.871  
  Call Number UA @ lucian @ c:irua:79163 Serial 1027  
Permanent link to this record
 
 
Author Nikolaev, A.V.; Michel, K.H. url  doi
openurl 
  Title Superexchange and electron correlations in alkali fullerides AC60, A=K, Rb, Cs Type A1 Journal article
  Year (down) 2005 Publication The journal of chemical physics Abbreviated Journal J Chem Phys  
  Volume 122 Issue 6 Pages 064310-64314  
  Keywords A1 Journal article; Condensed Matter Theory (CMT)  
  Abstract Superexchange interactions in alkali fullerides AC(60) are derived for C-60 molecular ions separated by interstitial alkali-metal ions. We use a multiconfiguration approach which comprises the lowest molecular orbital states of the C-60 molecule and the excited s and d states of the alkali-metal atom A. Interactions are described by the valence bond (Heitler-London) method for a complex (C-60 – A – C-60) – with two valence electrons. The electronic charge transfer between the alkali-metal atom and a neighboring C-60 molecule is not complete. The occupation probability of excited d and s states of the alkali atom is not negligible. In correspondence with the relative positions of the C-60 molecules and A atoms in the polymer crystal, we consider 180degrees and 90degrees (angle) superexchange pathways. For the former case the ground state is found to be a spin singlet separated from a triplet at similar to20 K. For T < 20 K there appear strong spin correlations for the 180degrees superexchange pathway. The results are related to spin lattice relaxation experiments on CsC60 in the polymerized and in the quenched cubic phase. (C) 2005 American Institute of Physics.  
  Address  
  Corporate Author Thesis  
  Publisher Place of Publication New York, N.Y. Editor  
  Language Wos 000226918100018 Publication Date 2005-02-02  
  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 0021-9606; ISBN Additional Links UA library record; WoS full record; WoS citing articles  
  Impact Factor 2.965 Times cited 11 Open Access  
  Notes Approved Most recent IF: 2.965; 2005 IF: 3.138  
  Call Number UA @ lucian @ c:irua:102740 Serial 3377  
Permanent link to this record
 
 
Author Nikolaev, A.V.; Michel, K.H. doi  openurl
  Title Ab initio approach to superexchange interactions in alkali doped fullerides AC60 Type P1 Proceeding
  Year (down) 2004 Publication AIP conference proceedings T2 – 18th International Winterschool/Euroconference on Electronic Properties, of Novel Materials, MAR 06-JUN 13, 2004, Kirchberg, AUSTRIA Abbreviated Journal  
  Volume Issue Pages 393-396  
  Keywords P1 Proceeding; Condensed Matter Theory (CMT)  
  Abstract The superexchange interactions between the fullerenes arise as a result of the electron transfer from the C-60 molecule to the alkali atom and back. We present a scheme, which is a configuration interaction approach based on the valence bond (Heitler-London) method. The effect of superexchange is described together with chemical bonding by constructing and solving a secular equation, rather than by using a perturbation treatment. We have considered 180degrees and 90degrees superexchange for the C-60 Cs-C-60 pathways. The calculations account for unusual electronic properties of polymer orthorhombic and quenched cubic phases of CsC60: two lines in nuclear magnetic resonance experiments, the development of a spin-singlet ground state and a decrease of magnetic susceptibility as T-->0.  
  Address  
  Corporate Author Thesis  
  Publisher Place of Publication New York Editor  
  Language Wos 000224699400085 Publication Date 2004-11-11  
  Series Editor Series Title Abbreviated Series Title  
  Series Volume 723 Series Issue Edition  
  ISSN 0-7354-0204-3 ISBN Additional Links UA library record; WoS full record; WoS citing articles  
  Impact Factor Times cited Open Access  
  Notes Approved Most recent IF: NA  
  Call Number UA @ lucian @ c:irua:103752 Serial 27  
Permanent link to this record
 
 
Author Nikolaev, A.V.; Michel, K.H. doi  openurl
  Title Many electron- and hole terms of molecular ions C60n\pm Type A1 Journal article
  Year (down) 2003 Publication Coupling In Chemistry And Physics Abbreviated Journal Adv Quantum Chem  
  Volume 44 Issue Pages 305-312  
  Keywords A1 Journal article; Condensed Matter Theory (CMT)  
  Abstract  
  Address  
  Corporate Author Thesis  
  Publisher Place of Publication New York, N.Y. Editor  
  Language Wos 000188940800019 Publication Date 2004-05-19  
  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 0065-3276; ISBN Additional Links UA library record; WoS full record; WoS citing articles  
  Impact Factor 1.196 Times cited 1 Open Access  
  Notes Approved Most recent IF: 1.196; 2003 IF: 0.375  
  Call Number UA @ lucian @ c:irua:104131 Serial 1942  
Permanent link to this record
 
 
Author Nikolaev, A.V.; Michel, K.H. url  doi
openurl 
  Title Symmetry lowering at the structural phase transitions in NpO2 and UO2 Type A1 Journal article
  Year (down) 2003 Publication Physical review : B : condensed matter and materials physics Abbreviated Journal Phys Rev B  
  Volume 68 Issue 5 Pages 054112-054112,7  
  Keywords A1 Journal article; Condensed Matter Theory (CMT)  
  Abstract The structural phase transitions with electric-quadrupole long-range order in NpO2 (Fm (3) over barm-->Pn (3) over barm) and UO2 (Fm (3) over barm-->Pa (3) over bar) are analyzed from a group theoretical point of view. In both cases, the symmetry lowering involves three quadrupolar components belonging to the irreducible representation T-2g (Gamma(5)) of O-h and condensing in a triple-q structure at the X point of the Brillouin zone. The Pa (3) over bar structure is close to Pn (3) over barm, but allows for oxygen displacements. The Pa (3) over bar ordering leads to an effective electrostatic attraction between electronic quadrupoles while the Pn (3) over barm ordering results in a repulsion between them. It is concluded that the Pn (3) over barm structure can be stabilized only through some additional process such as strengthening of the chemical bonding between Np and O. We also derive the relevant structure-factor amplitudes for Pn (3) over barm and Pa (3) over bar, and the effect of domains on resonant x-ray scattering experiments.  
  Address  
  Corporate Author Thesis  
  Publisher Place of Publication Editor  
  Language Wos 000185240100038 Publication Date 2003-08-29  
  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 0163-1829;1095-3795; ISBN Additional Links UA library record; WoS full record; WoS citing articles  
  Impact Factor 3.836 Times cited 15 Open Access  
  Notes Approved Most recent IF: 3.836; 2003 IF: NA  
  Call Number UA @ lucian @ c:irua:94847 Serial 3405  
Permanent link to this record
 
 
Author Nikolaev, A.V.; Michel, K.H. openurl 
  Title Molecular terms and optical transitions of C60n+/- molecular ions Type P1 Proceeding
  Year (down) 2002 Publication AIP conference proceedings T2 – 16th International Winterschool on Electronic Properties of Novel, Materials, MAR 02-09, 2002, KIRCHBERG, AUSTRIA Abbreviated Journal  
  Volume Issue Pages 417-420  
  Keywords P1 Proceeding; Condensed Matter Theory (CMT)  
  Abstract We have studied the molecular energy terms of the hole configurations (h(u)(+))(m), m=2,3,4,5 of C-60(m+) cations and the electronic configurations (t(1u))(n) n=2,3,4, as well as (t(1u))(n-1)t(1g) of the C-60(n-) anions. The lowest terms (within an energy span of 0.03 eV) for C-60(2+) are three triplets T-3(1g), (3)G(g), T-3(2g) and for C-60(3+) are three quartets T-4(1u), (4)G(u), T-4(2u), which favor Jahn-Teller distortions. For the ground state of C-60(2-) we find a triplet T-3(1g) in agreement with Hund's rules. Our method takes into account intramolecular direct and exchange multipolar Coulomb interactions.  
  Address  
  Corporate Author Thesis  
  Publisher Place of Publication New York Editor  
  Language Wos Publication Date 0000-00-00  
  Series Editor Series Title Abbreviated Series Title  
  Series Volume 633 Series Issue Edition  
  ISSN 0-7354-0088-1 ISBN Additional Links UA library record; WoS full record;  
  Impact Factor Times cited Open Access  
  Notes Approved Most recent IF: NA  
  Call Number UA @ lucian @ c:irua:103905 Serial 2187  
Permanent link to this record
 
 
Author Nikolaev, A.V.; Michel, K.H. doi  openurl
  Title Microscopic theory of quadrupolar oredring in TmTe Type A1 Journal article
  Year (down) 2001 Publication Physical review : B : condensed matter and materials physics Abbreviated Journal Phys Rev B  
  Volume 63 Issue Pages 1-10  
  Keywords A1 Journal article; Condensed Matter Theory (CMT)  
  Abstract  
  Address  
  Corporate Author Thesis  
  Publisher Place of Publication Lancaster, Pa Editor  
  Language Wos 000167402100025 Publication Date 2002-07-27  
  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 0163-1829;1095-3795; ISBN Additional Links UA library record; WoS full record; WoS citing articles  
  Impact Factor 3.836 Times cited 7 Open Access  
  Notes Approved Most recent IF: 3.836; 2001 IF: NA  
  Call Number UA @ lucian @ c:irua:36882 Serial 2033  
Permanent link to this record
 
 
Author Nikolaev, A.V.; Michel, K.H. doi  openurl
  Title Electronic structure and electric quadrupoles of a polymerized chain in solid AC60 Type A1 Journal article
  Year (down) 2001 Publication Solid state communications Abbreviated Journal Solid State Commun  
  Volume 117 Issue Pages 739-743  
  Keywords A1 Journal article; Condensed Matter Theory (CMT)  
  Abstract  
  Address  
  Corporate Author Thesis  
  Publisher Place of Publication New York, N.Y. Editor  
  Language Wos 000167538300010 Publication Date 2002-07-25  
  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 0038-1098; ISBN Additional Links UA library record; WoS full record; WoS citing articles  
  Impact Factor 1.554 Times cited 10 Open Access  
  Notes Approved Most recent IF: 1.554; 2001 IF: 1.381  
  Call Number UA @ lucian @ c:irua:36881 Serial 1009  
Permanent link to this record
 
 
Author Nikolaev, A.V.; Michel, K.H. doi  openurl
  Title Electric quadrupole interactions and the γ-α phase transition in Ce: the role of conduction electrons Type A1 Journal article
  Year (down) 2000 Publication European physical journal : B : condensed matter and complex systems Abbreviated Journal Eur Phys J B  
  Volume 17 Issue Pages 15-32  
  Keywords A1 Journal article; Condensed Matter Theory (CMT)  
  Abstract  
  Address  
  Corporate Author Thesis  
  Publisher Place of Publication Berlin Editor  
  Language Wos 000089339900004 Publication Date 2003-05-15  
  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 1434-6028; ISBN Additional Links UA library record; WoS full record; WoS citing articles  
  Impact Factor 1.461 Times cited 8 Open Access  
  Notes Approved Most recent IF: 1.461; 2000 IF: 2.077  
  Call Number UA @ lucian @ c:irua:34338 Serial 888  
Permanent link to this record
 
 
Author Nikolaev, A.V.; Michel, K.H. doi  openurl
  Title Quantum charge density fluctuations and the γ-α phase transition in Ce Type A1 Journal article
  Year (down) 1999 Publication European physical journal : B : condensed matter and complex systems Abbreviated Journal Eur Phys J B  
  Volume 9 Issue Pages 619-634  
  Keywords A1 Journal article; Condensed Matter Theory (CMT)  
  Abstract  
  Address  
  Corporate Author Thesis  
  Publisher Place of Publication Berlin Editor  
  Language Wos 000081615500009 Publication Date 2002-08-25  
  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 1434-6028; ISBN Additional Links UA library record; WoS full record; WoS citing articles  
  Impact Factor 1.461 Times cited 19 Open Access  
  Notes Approved Most recent IF: 1.461; 1999 IF: 1.705  
  Call Number UA @ lucian @ c:irua:28504 Serial 2774  
Permanent link to this record
 
 
Author Nikolaev, A.V.; Michel, K.H. url  doi
openurl 
  Title Microscopic theory of the rhombohedral phase and transition to the monoclinic phase of solid C70 Type A1 Journal article
  Year (down) 1996 Publication Physical review : B : condensed matter and materials physics Abbreviated Journal Phys Rev B  
  Volume 54 Issue 18 Pages 12733-12743  
  Keywords A1 Journal article; Condensed Matter Theory (CMT)  
  Abstract Starting from a model of microscopic interactions between C-70 molecules, we have developed a theory which describes the orientational dynamics and its coupling to lattice displacements in the rhombohedral phase of C-70 fullerite. The Landau free energy is calculated. We obtain a first-order phase transition to a monoclinic structure with the space group P2(1)/m. The transition is driven by the condensation of orientational quadrupoles at the F point of the Brillouin zone of the rhombohedral lattice. We find no evidence that the monoclinic structure is connected with the freezing in of orientations around the fivefold molecular axis. We calculate the lattice strains that are associated with the transition to the monoclinic structure. The theory is compared with a range of experimental data on the phase transition.  
  Address  
  Corporate Author Thesis  
  Publisher Place of Publication Lancaster, Pa Editor  
  Language Wos A1996VT68200028 Publication Date 2002-07-27  
  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 0163-1829;1095-3795; ISBN Additional Links UA library record; WoS full record; WoS citing articles  
  Impact Factor 3.736 Times cited 5 Open Access  
  Notes Approved no  
  Call Number UA @ lucian @ c:irua:16357 Serial 2034  
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