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@TECHREPORT{Eckold:849717,
      author       = {Eckold, G.},
      title        = {{UNISOFT}: a program package for lattice dynamical
                      calculations: user manual},
      volume       = {2639},
      number       = {Juel-2639},
      address      = {Jülich},
      publisher    = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
      reportid     = {FZJ-2018-03850, Juel-2639},
      series       = {Berichte des Forschungszentrums Jülich},
      pages        = {X, 117 p.},
      year         = {1992},
      abstract     = {Lattice-dynamical investigations provide a powerful tool
                      for the determination of interatomic forces and chemical
                      bonding in crystals. In general the extraction of,
                      say,potential parameters from phonon dispersion curves, as
                      determined experimentally, is possible with the help of
                      model calculations only. Phonons which are cooperative
                      excitations in many-body systems provide informations about
                      interactions within the whole crystal. A quantitative
                      interpretation of single phonons is therefore restricted to
                      very simple crystal structures. In general, however,
                      unambigious statements about interatomic forces require the
                      knowledge of a good number of the phonon branches, at least
                      in the symmetry directions. Often, the determination of
                      phonon dispersion curves is a rather hard task since a
                      crystal with N particles per unit cell exhibits as many as
                      3N phonon branches. The only experimental method which
                      allows the detection of phonons at arbitrary points within
                      the Brillouin zone is the inelastic neutron scattering.
                      Again, model calculations are very useful and sometimes even
                      necessary in order to find phonons experimentally since
                      phonon intensities vary strongly from one Brillouin zone to
                      another and are determined by the corresponding
                      eigenvectors. For complex structures, model calculations and
                      neutron scattering experiments are thus complementary. The
                      determination of interatomic forces in crystals requires
                      both, the theoretical and the experimental approach which
                      need to go hand in hand. The three-axes spectrometer UNIDAS
                      at the FRJ-2 reactor at Jülich is available to external
                      users and is especially designed to meet the requirements
                      for phonon investigations. Details of this machine are
                      described in the UNIDAS-Handbuch [1]. In the present paper
                      we report an the complement to this spectrometer, namely the
                      computer program package UNISOFT which allows to perform
                      model calculations an phonon dispersion in general
                      structures with up to 20 particles per primitive cell.
                      UNISOFT has been developed in order to provide a tool for
                      the optimization of experiments as well as for a first
                      interpretation of the results. Certainly, a general
                      lattice-dynamical program cannot deal with the most complex
                      models for interatomic interactions. Until now the standard
                      models such as $\bullet$ Born-von Kärmän model
                      (longitudinal and transverse springs) $\bullet$ Born-Mayer
                      potential $\bullet$ Lennard-Jones potentialvan der Waals
                      potential $\bullet$ Coulomb potential (Ewald's method of
                      summation) $\bullet$ shell model are implemented. The
                      interaction between each pair of atoms can be chosen
                      individually as an arbitrary combination of these model
                      potentials. More sophisticated models must be developed by
                      the user and are beyond the scope of UNISOFT as a
                      universally applicable lattice-dynamical program. Special
                      attention has been paid to the handling of this program
                      package by external users. Offering the possibility of a
                      tailored interatomic interaction set-up for each individual
                      substance under consideration, the system is rather complex,
                      of course.Universality of the programs, however, does not
                      exclude an easy mode of operation. Thus, UNISOFT can indeed
                      be used in combination with UNIDAS by experimenters which
                      are not familiar with details of lattice-dynamical
                      calculations and the interpretation of phonon dispersion
                      curves. This combination of software and hardware is able to
                      simplify the determination of interatomic forces in crystals
                      even for nonspecialists. Chapter 2 of this report briefly
                      reviews the theoretical background of lattice dynamics in
                      the harmonic approximation along with group-theoretical
                      considerations and symmetry constraints to the dynamical
                      matrix. The response of a phonon system in neutron
                      scattering experiments is also discussed. In section 3 the
                      global structure of the program package is displayed before
                      a detailed description of the individual programs is given
                      in chapter 4. Section 5 deals with computer requirements.
                      Some possible extensions of this program system are
                      discussed in chapter 6. In order to illustrate all
                      information available with UNISOFT, an example for a
                      complete treatment of a crystal structure within this
                      program system is presented in appendix A. Finally, a
                      comprehensive list of all input cards, the alphabetical list
                      of subroutines, the subroutine reference list and the list
                      of symbols used in this manual are given in the appendices
                      B, C, D and E. Concerning the notation, matrices are denoted
                      by bold printed capital letters and vectors are represented
                      by bold printed lower case letters.},
      cin          = {PRE-2000},
      cid          = {I:(DE-Juel1)PRE2000-20140101},
      pnm          = {899 - ohne Topic (POF3-899)},
      pid          = {G:(DE-HGF)POF3-899},
      typ          = {PUB:(DE-HGF)3 / PUB:(DE-HGF)29},
      url          = {https://juser.fz-juelich.de/record/849717},
}