Matrix Product Toolkit | Main / TutorialShort

Short tutorial

Once you have your lattice file generated you need an initial state with mp-random to start the ground state calculation:

mp-random -l lattice -o gs-init

In case you are using symmetries you need to specify them via e.g. -q 30,0 (N=30, Sz=0).

Note that on 2007-08-16, a bug was found in mp-random. It accidentally always took the 4th parameter as the output filename, rather than the -o option. The above line accidentally works, because 'gs-init' happens to be the 4th parameter. It wouldn't work properly if you tried mp-random -l lattice -q 30,0 -o gs-init. (It would write the wave function to the file named '30,0') This is now fixed. -> Ian

Now we set up the dmrg calculation and then run it.

mp-dmrg-init -H lattice:H -w gs-init -c dmrg.conf -o gs
mp-dmrg-resume gs

The result is a file called gs.psi.##, ## being the number of sweeps performed, which holds the calculated ground state. With that state you can calculate all sorts of expectation values using mp-[local]expectation[2] and correlations using mp-localcorrelation which should be preferred over mp-correlation

Note on SU(2) symmetric models

When creating the Hamiltonian nearest neighbour hopping terms need an additional factor of sqrt(2) compared to an U(1) model.
One needs to multiply all S*S correlations with -sqrt(3)!