Ralph H. Scheicher

Publications (69) View all

• Source

  Available from: espace.cern.ch

  Article: First principles electronic structure investigation of order of singlet and triplet states of oxyhemoglobin and analysis of possible influence of muon trapping

  S. R. Badu, R. H. Pink, R. H. Scheicher, Archana Dubey, N. Sahoo, K. Nagamine, T. P. Das
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  ABSTRACT: Interest in the possibility of magnetic character for oxyhemoglobin (OxyHb) has been recently stimulated by the observations of muon spin-lattice relaxation effects studied (Nagamine et al., Proc Jpn Acad Ser B Phys Biol Sci 83:120–126, 2007) with the muon-spin rotation (μSR) technique. In view of this, we have carried out first-principles electronic structure investigations involving Hartree–Fock theory combined with many body perturbation effects for the singlet and triplet states of OxyHb. Our results indicate that using two recent x-ray structural data (Paoli et al., J Mol Biol 256:775, 1996; Park et al., J Mol Biol 360:690, 2006) for OxyHb, for only Hartree–Fock theory without many-body effects included, the singlet state lies above the triplet state by energies of about 0.08 and 0.13 a.u. for the two structures in Paoli et al. (J Mol Biol 256:775, 1996) and Park et al. (J Mol Biol 360:690, 2006). Incorporation of many-body effects by the perturbation method reverses the order, with the triplet state located 0.18 and 0.14 a.u. above the singlet state for the structures in Paoli et al. (J Mol Biol 256:775, 1996) and Park et al. (J Mol Biol 360:690, 2006). Physical reasons for these relative orderings of the singlet and triplet states will be discussed. It is clear that OxyHb by itself would be in a singlet state at room temperature or below, since from our calculation, the triplet state lies about KT above the singlet state with T having the value of 44,098 K and 56,449 K for the two structural data in Paoli et al. (J Mol Biol 256:775, 1996) and Park et al. (J Mol Biol 360:690, 2006). As regards the muon spin-lattice relaxation effects obtained by recent μSR measurements (by Nagamine et al., Proc Jpn Acad Ser B Phys Biol Sci 83:120–126, 2007) at room temperature, the sensitive dependence of the singlet-triplet separation on many-body effects in our investigation suggests that it is possible that the singlet-triplet separation could be reversed or reduced significantly when a muon is trapped near an oxygen atom of the oxygen molecule, allowing the triplet to be occupied at room temperature and lead to significant muon spin-lattice relaxation. KeywordsOxyhemoglobin–Magnetic susceptability–Singlet–Triplet–Muon–Muon spin relaxation–Hartree–Fock–Many body
  Hyperfine Interactions 04/2012; 197(1):331-340. · 0.21 Impact Factor
• Source

  Available from: Lee Chow

  Article: First-principles cluster study of electronic structures, locations and hyperfine interactions of isolated atoms and ions in silicon

  R. H. Pink, S. R. Badu, R. H. Scheicher, Lee Chow, M. B. Huang, T. P. Das
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  ABSTRACT: The electronic structures of the dilute transition metal (TM) impurities, V2 + , Cr + , Mn2 + , and Mn0 in silicon have been studied using the Hartree–Fock (HF) procedure combined with many-body perturbation theory (MBPT). The systems studied involved the TM impurities at the hexagonal interstitial (H i ), tetrahedral interstitial (T i ) and substitutional (S) locations. Investigations of the binding energy and local potential energy surface of the TM impurity-Si systems indicate that the TM impurities are binding at the T i location. Hyperfine interaction constants (A) of the TM impurities at the T i and S sites are presented and compared with available experimental results (Woodbury and Ludwig, J Phys Rev 117:102, 1960a, Phys Rev Lett 5:98, b) from Electron Paramagnetic Resonance (EPR) measurements. KeywordsMagnetic semiconductors–Transition metal impurities–Binding energies–Trapping sites–Hyperfine interactions
  Hyperfine Interactions 04/2012; 197(1):37-41. · 0.21 Impact Factor
• Article: Ab initio Study of Lithium Doped Graphane for Hydrogen Storage

  T. Hussain, Biswarup Pathak, Tuhina A. Mark, C. M. Araujo, R. H. Scheicher, R. Ahuja
  Europhysics Letter. 01/2011; EPL:27013.
• Source

  Available from: Muhammad Ramzan

  Article: Structural and energetic analysis of the hydrogen storage materials LiNH_ {2} BH_ {3} and NaNH_ {2} BH_ {3} from ab initio calculations

  M. Ramzan, F. Silvearv, A. Blomqvist, R. H. Scheicher, S. Lebègue, R. Ahuja
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  ABSTRACT: Ammonia borane (NH3BH3) possesses many appealing properties as a hydrogen storage material; however, the release of trace amounts of borazine during the desorption process is troublesome. Recently, it was found that substitution of one of the H atoms in the NH3 group by Li or Na could significantly improve the hydrogen desorption properties. The resulting lithium amidoborane (LiNH2BH3) and sodium amidoborane (NaNH2BH3) compounds have been studied by us using density-functional theory. Specifically, we have succeeded in determining the detailed crystal structures of LiNH2BH3 and NaNH2BH3, including the atomic positions in their respective unit cells. Calculated hydrogen removal energies of the hydrogen release reactions are found to be in good agreement with the experimental trend.
  Physical Review B 04/2009; 79(13). · 3.69 Impact Factor
• Article: Stability of ferromagnetic phase in Fe-doped AlH3

  J. Nisar, R. H. Scheicher, X. Peng, R. Ahuja
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  ABSTRACT: We have carried out a systematic theoretical investigation of Fe-doped AlH3 to study its magnetic properties and to assess the stability of the ferromagnetic phase in this material. All calculations were performed using the projector augmented-wave method and generalized-gradient approximation (GGA) as well as GGA+U. The magnetic moment is found to be constant at 1.1 μB per Fe-atom in the ferromagnetic configuration for distances between adjacent Fe atoms varying from 3.25°A to 7.41°A. We conclude that the ferromagnetic phase in Fe-doped AlH3 is stable both for near and far configurations of Fe. The stability of the ferromagnetic phase is due to the holes created by Fe-doping and the larger level splitting of the interacting gap states within the ferromagnetic phase.
  EPL (Europhysics Letters) 01/2009; 85:67006. · 2.17 Impact Factor