calculates dispersion and V transformation matrix using linear spin wave theory
[omega, V] = CORESPEC(obj, hkl, 'option1', value1 ...)
Spin wave dispersion and spin-spin correlation function is calculated at
the reciprocal space points k. The function can deal with arbitrary
magnetic structure and magnetic interactions as well as single ion
anisotropy and magnetic field.
If the magnetic ordering wavevector is non-integer, the dispersion is
calculated using a coordinate system rotating from cell to cell. In this
case the Hamiltonian has to fulfill this extra rotational symmetry.
Input:
obj Input structure, sw class object.
hkl Defines the Q points where the spectra is calculated, in
reciprocal lattice units, size is [3 nHkl]. Q can be also
defined by several linear scan in reciprocal space. In this
case hkl is cell type, where each element of the cell
defines a point in Q space. Linear scans are assumed
between consecutive points. Also the number of Q points can
be specified as a last element, it is 100 by defaults. For
example: hkl = {[0 0 0] [1 0 0] 50}, defines a scan along
(h,0,0) from 0 to 1 and 50 Q points are calculated along
the scan.
Options:
fitmode Speedup (for fitting mode only), default is false.
notwin If true, the spectra of the twins won't be calculated.
Default is false.
sortMode The spin wave modes will be sorted if true. Default is
true.
optmem Parameter to optimise memory usage. The list of hkl values
will be cut into optmem number of pieces and will be
calculated piece by piece to decrease memory usage. Default
of optmem is zero, when the number of slices are determined
automatically from the available free memory.
tol Tolerance of the incommensurability of the magnetic
ordering wavevector. Deviations from integer values of the
ordering wavevector smaller than the tolerance are
considered to be commensurate. Default value is 1e-4.
omega_tol Tolerance on the energy difference of degenerate modes when
diagonalising the quadratic form, default is 1e-5.
hermit Method for matrix diagonalization:
true J.H.P. Colpa, Physica 93A (1978) 327,
false R.M. White, PR 139 (1965) A450.
Colpa: the grand dynamical matrix is converted into another
Hermitian matrix, that will give the real
eigenvalues.
White: the non-Hermitian g*H matrix will be diagonalised,
that is not the elegant method.
Advise:
Always use Colpa's method, except when small imaginary
eigenvalues are expected. In this case only White's method
work. The solution in this case is wrong, however by
examining the eigenvalues it can give a hint where the
problem is.
Default is true.
nSlice Parameter to optimise memory usage. The list of hkl values
will be cut into nSlice pieces and will be calculated piece
by piece to decrease memory usage. Default is zero, when
the number of slices are determined automatically from the
available free memory.
onlyV Calculate only the dispersion and the V linear
transformation matrices. The V matrices transform between
the original magnon operators and the normal magnon
operators.
Output:
spectra is a structure, with the following fields:
omega Calculated spin wave dispersion, dimensins are
[nMode nHkl], where nMagExt is the number of magnetic
atoms in the extended unit cell.
Sab Dynamical structure factor, dimensins are
[3 3 nMode nHkl]. Each (:,:,i,j) submatrix contains the
9 correlation functions: Sxx, Sxy, Sxz, etc.
V Optional output, calculated if 'onlyV' option is true (in
that case Sab is not calculated). Dimensions are
[nMode nMode nHkl].
nMode is the number of magnetic mode. For commensurate structures it is
double the number of magnetic atoms in the magnetic cell/supercell. For
incommensurate structures this number is tripled due to the appearance of
the (Q+/-km) Fourier components in the correlation functions.
If several twins exist in the sample, omega and Sab are packaged into a
cell, that contains nTwin number of matrices.
hkl Contains the input Q values, dimensins are [3 nHkl].
hklA Same Q values, but in reciproc Angstrom units in the
lab coordinate system, dimensins are [3 nHkl].
incomm Whether the spectra calculated is incommensurate or not.
obj The copy of the input obj.
See also SW, SW.SPINWAVESYM, SW_NEUTRON, SW_POL, SW.POWSPEC, SW.OPTMAGSTR.