Variational Monte-Carlo for Gutzwiller-Projected Wavefunctions implementation {#mainpage}

The software main objective is to provide an efficient way of calculating many-body wavefunction $|\psi\rangle$ overlaps with real space spin configuration state $|\alpha\rangle$. Its main components are:

• The wavefunction $|\psi\rangle$ is a trial ground state or excited state. Different such wavefunctions are implemented and inherit from the WaveFunction object.
• The real space spin configuration $|\alpha\rangle$ are states upon which a Monte Carlo sampling is performed. They are implemented in the LatticeState object.
• The overlap $\langle\psi|\alpha\rangle$ is a Slater determinant and is efficiently implemented into the SlaterDeterminant object.
• The Monte Carlo random walk generator (i. e. the step generator and the Monte Carlo weight definition) is implemented in the objects inheriting from the Stepper object.
• Different measurements can be performed simultaneously during the Monte Carlo sampling. These inherit from the Quantity object.
• Finally the Monte Carlo itself is implemented into the MetroMC object (for Metropolis Monte Carlo).

##Requirements This software has been built in various linux distributions. The requirements are:

• A BLAS/LAPACK library
• The HDF5 library
• cmake

##Optional requirements

• The GNU Scientific Library
• An MPI implementation
• doxygen to build the documentation

##Install

1. Make a build directory, for instance directly in the main source folder

   :~/.../sourcedir$ mkdir build
   

2. Configure the build toolchain.

   :~/.../sourcedir$ cd build
   :~/.../sourcedir/build$ cmake ..
   

3. Review the options to check they meet your environment

   :~/.../sourcedir/build$ ccmake .
   

   In particular:

   • If you don't have the GNU Scientific Library, please choose "USE_RNG_GSL=NO" and "USE_RNG_STD=YES". Doing so you will use the standard random number generator (probably a bad idea).
   • If you don't have an MPI implementation installed, you must pick "USE_MPI=NO".
   • Set the installation directory (default /usr/local) to some place you have write access (or you can do sudo)

4. Build the software and install it

   :~/.../sourcedir/build$ make
   :~/.../sourcedir/build$ make install
   

   This produces the "vmc" executable and installs python packages (in the installation directory) that you can use for postprocessing (Make sure python knows where to find them).

5. The documentation may optionally be built as well by

   :~/.../sourcedir/build$ make doc
   

##Run The "vmc" executable, if called without arguments, will list all the possible options. A typical example would be:

    :~/.../installdir$ vmc --neel=0.1 --phi=0.25 --L=8\
    --samples=1 --samples_saves=1 --samples_saves_stat=100000 --therm=200\
    --channel=groundstate --meas_projheis --meas_stagmagn --meas_statspinstruct

• --neel and --phi options relate to some variational parameters (see our publication above)
• --L=8 sets the system size to 8x8
• --samples=1 sets the number of different samples (per thread) to gather statistics for.
• --samples_saves=1 sets the number of times the gathered statistics must be saved.
• --samples_saves_stat=100000 sets the amount of statistics of each save.
• --therm=200 sets the thermalization steps to 200*L*L
• --channel=groundstate asks to measure the groundstate trial wavefunction.
• --meas_projheis asks to measure the (projected) Heisenberg Hamiltonian.
• --meas_stagmagn asks to measure the staggered magnetization.
• --meas_statspinstruct asks to measure the static spin structure factor.

A python script performing an example calculation may be found in the source root directory.

##Output The different outputs are in the HDF5 format, one file per quantity. The HDF5 files gather all the statistics of each quantity. Some postprocessing tools are provided in python.

##License The Software is distributed under the MIT license.