message: UI-QT: bugfix for n_basis_atoms > 1.
  mu_s is then an array and the API function needs to be used accordingly.
diff: #include "HamiltonianHeisenbergPairsWidget.hpp"
  #include <Spirit/System.h>
  +#include <Spirit/Geometry.h>
  #include <Spirit/Chain.h>
  #include <Spirit/Collection.h>
  #include <Spirit/Log.h>
  @@ -55,7 +56,9 @@ void HamiltonianHeisenbergPairsWidget::updateData()
  void HamiltonianHeisenbergPairsWidget::Load_Contents()
  {
  - float d, vd[3], mu_s;
  + float d, vd[3];
  + int n_basis_atoms = Geometry_Get_N_Basis_Atoms(state.get());
  + std::vector<float> mu_s(n_basis_atoms);
  // Boundary conditions
  bool boundary_conditions[3];
  @@ -65,8 +68,8 @@ void HamiltonianHeisenbergPairsWidget::Load_Contents()
  this->checkBox_aniso_periodical_c->setChecked(boundary_conditions[2]);
  // mu_s
  - Hamiltonian_Get_mu_s(state.get(), &mu_s);
  - this->lineEdit_muSpin_aniso->setText(QString::number(mu_s));
  + Hamiltonian_Get_mu_s(state.get(), mu_s.data());
  + this->lineEdit_muSpin_aniso->setText(QString::number(mu_s[0]));
  // External magnetic field
  Hamiltonian_Get_Field(state.get(), &d, vd);
  