Dear ALPS team,

I am trying to obtain magnetization curve of anisotropic XY model on frustrated diamond spin chain in transverse magnetic field (m^x) using full diagonalization. For this purpose I have prepared such input file for delta=1.5;
                
LATTICE="lattice_diamond"
MODEL="spin"
LATTICE_LIBRARY="lattice-diamond.xml"
local_S=1/2

Jxy1      = 0.85
Jxy2    = 3.0
Jxy3      = 1.15

Jz1      = 1.275
Jz2     = 4.5
Jz3      = 1.725

L       = 2
T       = 0.001

{Gamma =4;}
{Gamma =4.05;}
{Gamma =4.1;}
{Gamma =4.15;}
{Gamma =4.2;}
{Gamma =4.25;}
{Gamma =4.3;}
{Gamma =4.35;}
{Gamma =4.4;}
{Gamma =4.45;}
{Gamma =4.5;}
{Gamma =4.55;}
{Gamma =4.6;}
{Gamma =4.65;}
{Gamma =4.7;}
{Gamma =4.75;}
{Gamma =4.8;}
{Gamma =4.85;}
{Gamma =4.9;}
{Gamma =4.95;}
{Gamma =5;}
{Gamma =5.05;}
{Gamma =5.1;}
{Gamma =5.15;}
{Gamma =5.2;}
{Gamma =5.25;}
{Gamma =5.3;}
{Gamma =5.35;}
{Gamma =5.4;}
{Gamma =5.45;}
{Gamma =5.5;}
{Gamma =5.55;}
{Gamma =5.6;}
{Gamma =5.65;}
{Gamma =5.7;}
{Gamma =5.75;}
{Gamma =5.8;}
{Gamma =5.85;}
{Gamma =5.9;}
{Gamma =5.95;}
{Gamma =6;}

lattice-diamond.xml is:

<LATTICES>
<LATTICEGRAPH name="lattice_diamond">
<FINITELATTICE>
<LATTICE dimension="1">
<BASIS>
<VECTOR>1</VECTOR>
</BASIS>
</LATTICE>
<PARAMETER name="L"/>
<EXTENT size="L"/>
<BOUNDARY type="periodic"/>
</FINITELATTICE>
<UNITCELL dimension="1" vertices="3">
<VERTEX id="1" type="0">
</VERTEX>
<VERTEX id="2" type="0">
</VERTEX>
<VERTEX id="3" type="0">
 </VERTEX>
<EDGE type="2">
<SOURCE vertex="1"/>
<TARGET vertex="2"/>
</EDGE>
<EDGE type="3">
<SOURCE vertex="1"/>
<TARGET vertex="3"/>
</EDGE>
<EDGE type="1">
<SOURCE vertex="2"/>
<TARGET vertex="3"/>
</EDGE>
<EDGE type="3">
<SOURCE vertex="3"/>
<TARGET vertex="2" offset="1"/>
</EDGE>
<EDGE type="1">
<SOURCE vertex="3"/>
<TARGET vertex="1" offset="1"/>
</EDGE>
</UNITCELL>
</LATTICEGRAPH>
</LATTICES>

It works perfect for L=2 (6 sites), but I cant obtain correct magnetization curve for L=3 (9 sites) or L= 4 (12 sites) etc. Would you be so kind to explain me why it works well for small chain and worse for slightly larger chain?

Best regards,

Olesia Krupnitska