The module phonon allows to consider the phononic degrees of freedom in McPhas. The single ion input file for an oscillating atom has to have the following format:
#!MODULE=phonon #<!--mcphase.sipf--> # # phonon # MODPAR1=mass of atom in units of m0 (atomic mass unit=1.660539e-27 kg) # #----------- MODPAR1=57 # mass in(m0) MODPAR2=7 # Kxx MODPAR3=7 # Kyy MODPAR4=8 # Kzz MODPAR5=0 # Kxy in (meV) MODPAR6=0 # Kxz MODPAR7=0 # Kyz #------------------------------------------------------- # Neutron Scattering Length (10^-12 cm) (can be complex) #------------------------------------------------------- SCATTERINGLENGTHREAL=0.769 SCATTERINGLENGTHIMAG=0 # ... note: - if an occupancy other than 1.0 is needed, just reduce # the scattering length linear accordingly SCATTERINGLENGTHREAL=0.945 SCATTERINGLENGTHIMAG=0
Thus the single ion property file contains the matrix
, the matrix
decribing the
forces between
different ions 
and 
have to be given in the file mcphas.j, which could
look like:
# #<!--mcphase.mcphas.j--> ************************************************************* # Lattice Constants (A) #! a=4.047 b=4.047 c=9.612 alpha= 90 beta= 90 gamma= 90 #! r1a= 1 r2a= 0 r3a= 0.5 #! r1b= 0 r2b= 1 r3b= 0.5 primitive lattice vectors [a][b][c] #! r1c= 0 r2c= 0 r3c= 0.5 #! nofatoms=1 nofcomponents=3 number of atoms in primitive unit cell/number of components of each spin #********************************************************************* #! da= 0 [a] db= 0 [b] dc= 0 [c] nofneighbours=2 diagonalexchange=1 sipffilename=phonon.sipf #da[a] db[b] dc[c] Jaa[meV] Jbb[meV] Jcc[meV] Jab[meV] Jba[meV] Jac[meV] Jca[meV] Jbc[meV] Jcb[meV] 0 0 1 1.1 1.1 1.1 0 0 -1 1.1 1.1 1.1 #*********************************************************************
It is planned that these files should be created automatically from the output of DFT programs. [to be done]
If crystal field - phonon coupling is to be input, magnetic ions may be added to mcphas.j. They should not be placed at exactly the same position as the phonon atoms - i.e. da db dc should be chosen (slightly) different to enable the mcphas.j loader to identify which is which.
The coupling between phononic and crystal field degrees of freedom should be derived from
. This could be done
using the program pointc and makenn applying small differential changes to
the atomic positions in the unit cell in order to evaluate the gradient of the crystal field
parameters. [efficient program to do this task is to be written]