Hi Matthias, Thanks for your reply. Below is the simplest implementation that I could cook up with free spinless fermions on two sites with *directed* bonds. The output of sparsediag, including the error, is -------------------------------------------------------------------------- parsing task files ... Starting task 1. Quantumnumber N going from 0 to 2 with increment 1 Cannot evaluate expression t# * 1 * 1 -------------------------------------------------------------------------- My short source is attached below. I hope that it's a quick task to figure out what is wrong with the implementation. Thanks in advance, Alex Alexandru Petrescu / Physics Department, Yale University Code attachment In <alps-dir>/lib/xml/lattices.xml I added ------------------------------------------------------------------------ <GRAPH name="my 2-site" vertices="2"> <EDGE source="1" target="2" type="1"/> <EDGE source="2" target="1" type="2"/> </GRAPH> ------------------------------------------------------------------------- In <alps-dir>/lib/xml/models.xml, ------------------------------------------------------------------------ <HAMILTONIAN name="free spinless fermions with bondterm type"> <PARAMETER name="mu" default="0"/> <PARAMETER name="t" default="1"/> <BASIS ref="spinless fermion"/> <SITETERM site="i"> <PARAMETER name="mu#" default="mu"/> -mu#*n(i) </SITETERM> <BONDTERM type="1" source="i" target="j"> <PARAMETER name="t#" default="t"/> -t#*(cdag(i)*c(j)+cdag(j)*c(i)) </BONDTERM> <BONDTERM type="2" source="i" target="j"> <PARAMETER name="t#" default="t"/> -t#*(cdag(i)*c(j)+cdag(j)*c(i)) </BONDTERM> </HAMILTONIAN> ------------------------------------------------------------------------- The parameter file is LATTICE="my 2-site"; ------------------------------------------------------------------------- MODEL="free spinless fermions with bondterm type" NUMBER_EIGENVALUES = 1 CONSERVED_QUANTUMNUMBERS="N" MEASURE_ENERGY = true t = 3.0; V = 0.0; {mu=0.00} -------------------------------------------------------------------------- If instead "spinless fermions" with V=0 are used in the parameter file, sparsediag works, but all energies come out to be 0.