spinw.newcell method

Syntax

newcell(obj,Name,Value)

T = newcell(obj,Name,Value)

Description

T = newcell(obj,Name,Value) redefines the unit cell using new basis vectors. The input three basis vectors are in lattice units of the original cell and define a parallelepiped. The atoms from the original unit cell will fill the new unit cell and if the two cells are compatible the structure won’t change. The magnetic structure, bonds and single ion property definitions will be erased. The new cell will have different reciprocal lattice, however the original reciprocal lattice units will be retained automatically. To use the new reciprocal lattice, set the 'keepq' option to false. In the default case the spinw.spinwave function will calculate spin wave dispersion at reciprocal lattice points of the original lattice. The transformation between the two lattices is stored in spinw.unit.qmat.

Examples

In this example we generate the triangular lattice antiferromagnet and convert the hexagonal cell to orthorhombic. This doubles the number of magnetic atoms in the cell and changes the reciprocal lattice. However we set 'keepq' parameter to true to able to index the reciprocal lattice of the orthorhombic cell with the reciprocal lattice of the original hexagonal cell. To show that the two models are equivalent, we calculate the spin wave spectrum on both model using the same rlu. On the orthorhombic cell, the \(Q\) value will be converted automatically and the calculated spectrum will be the same for both cases.

tri = sw_model('triAF',1)
tri_orth = copy(tri)
tri_orth.newcell('bvect',{[1 0 0] [1 2 0] [0 0 1]},'keepq',true)
tri_orth.gencoupling
tri_orth.addcoupling('bond',1,'mat','J_1')
newk = ((tri_orth.unit.qmat)*tri.magstr.k')'
tri_orth.genmagstr('mode','helical','k',newk,'S',[1 0 0]')
plot(tri_orth)

subplot(2,1,1)
sw_plotspec(sw_egrid(tri.spinwave({[0 0 0] [1 1 0] 501})),'mode','color','dE',0.2)
subplot(2,1,2)
spec = tri_orth.spinwave({[0 0 0] [1 1 0] 501});
sw_plotspec(sw_egrid(tri_orth.spinwave({[0 0 0] [1 1 0] 501})),'mode','color','dE',0.2)

sw_plotspec(sw_egrid(tri_orth.spinwave({[0 0 0] [1 1 0] 501})),'mode','color','dE',0.2)

Input Arguments

obj: spinw object.

Name-Value Pair Arguments

'bvect': Defines the new lattice vectors in the original lattice coordinate system. Cell with the following elements {v1 v2 v3} or a \([3\times 3]\) matrix with v1, v2 and v3 as column vectors: [v1 v2 v3]. Default value is eye(3) for indentity transformation.
'bshift': Row vector that defines a shift of the position of the unit cell. Default value is [0 0 0].
'keepq': If true, the reciprocal lattice units of the new model will be the same as in the old model. This is achieved by storing the transformation matrix between the new and the old coordinate system in spinw.unit.qmat and applying it every time a reciprocal space definition is invoked, such as in spinw.spinwave. Default value is false.

Output Arguments

T

Transformation matrix that converts \(Q\) points (in reciprocal lattice units) from the old reciprocal lattice to the new reciprocal lattice as follows:

Qrlu_new = T * Qrlu_old