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Copyright (C) 2013-2016 Sebastian Wouters
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.. index:: Matrix elements
.. index:: psi4
.. index:: pyscf
``CheMPS2::Hamiltonian``
========================
There are several ways to feed matrix elements to CheMPS2. They are explained below in detail. Because CheMPS2 is a spin-adapted code, it can only handle spatial orbitals. It is hence not possible to use different orbitals for :math:`\uparrow` and :math:`\downarrow` electrons.
#. The ``CheMPS2::Hamiltonian`` object is able to read in FCIDUMP files. The ``fcidump`` plugin to `psi4 <http://www.psicode.org/>`_ allows to generate such FCIDUMP files.
#. The ``savehdf`` plugin to `psi4 <http://www.psicode.org/>`_ fills a ``CheMPS2::Hamiltonian`` object, and saves the matrix elements to disk in HDF5 format, taking into account their eightfold permutation symmetry.
#. Users can also generate matrix elements themselves, and feed them to the ``CheMPS2::Hamiltonian`` object.
psi4 ``fcidump`` plugin
-----------------------
The ``CheMPS2::Hamiltonian`` object is able to read in FCIDUMP files:
.. code-block:: c++
CheMPS2::Hamiltonian::Hamiltonian( const string filename, const int psi4groupnumber )
The variable ``filename`` should contain the path to the FCIDUMP file, and the variable ``psi4groupnumber`` should be the group number of the abelian point group with real-valued character table as defined in `psi4 <http://www.psicode.org/>`_. The conversion table is provided here:
+--------------+----+----+----+----+----+-----+-----+-----+
| Group name | c1 | ci | c2 | cs | d2 | c2v | c2h | d2h |
+--------------+----+----+----+----+----+-----+-----+-----+
| Group number | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
+--------------+----+----+----+----+----+-----+-----+-----+
FCIDUMP files can for example be generated by molpro, or by a plugin to `psi4 <http://www.psicode.org/>`_. The plugin has been tested on `psi4-0.5 <https://github.com/psi4/psi4/releases/tag/0.5>`_ (released February 17, 2016).
To make use of this feature, build `psi4 <http://www.psicode.org/>`_ with the plugin option ``ENABLE_PLUGINS=ON``, and then run:
.. code-block:: bash
$ cd /mypsi4plugins
$ psi4 --new-plugin fcidump
$ cd fcidump
Now, replace the file ``fcidump.cc`` with ``/sourcefolder/chemps2/integrals/psi4plugins/fcidump.cc``. To compile the plugin, run:
.. code-block:: bash
$ make
An example input file to generate a FCIDUMP file:
.. literalinclude:: N2.fcidump.in
This file (``N2.fcidump.in``) should be placed in the folder ``/mypsi4plugins/fcidump/``. The FCIDUMP file can then be generated with:
.. code-block:: bash
$ cd /mypsi4plugins/fcidump
$ psi4 N2.fcidump.in N2.fcidump.out
$ less N2.CCPVDZ.FCIDUMP
Examples of output generated with this plugin can be found in ``/sourcefolder/chemps2/tests/matrixelements/``.
psi4 ``savehdf`` plugin
-----------------------
The ``CheMPS2::Hamiltonian`` object is able to read in HDF5 files generated by a plugin to `psi4 <http://www.psicode.org/>`_. The plugin has been tested on `psi4-0.5 <https://github.com/psi4/psi4/releases/tag/0.5>`_ (released February 17, 2016). It stores all unique matrix elements (remember that there is eightfold permutation symmetry) in binary form with HDF5.
To make use of this feature, build `psi4 <http://www.psicode.org/>`_ with the plugin option ``ENABLE_PLUGINS=ON``, and then run:
.. code-block:: bash
$ cd /mypsi4plugins
$ psi4 --new-plugin savehdf
$ cd savehdf
Now, replace the file ``savehdf.cc`` with ``/sourcefolder/chemps2/integrals/psi4plugins/savehdf.cc``. To compile the plugin, the Makefile should be adjusted. Change the line
.. code-block:: bash
$(CXX) $(LDFLAGS) -o $@ $^ $(CXXDEFS)
to
.. code-block:: bash
$(CXX) $(LDFLAGS) -o $@ $^ $(CXXDEFS) -lchemps2
Remember to add the library and include paths to the Makefile as well, if ``libchemps2`` is not installed in a standard location. For debian/sid, the HDF5 headers are located in the folder ``/usr/include/hdf5/serial/``. It might be necessary to add it to the ``INCLUDES`` variable in the Makefile.
To compile the plugin, run:
.. code-block:: bash
$ make
An example input file to use the ``savehdf`` plugin:
.. literalinclude:: N2.savehdf.in
This file (``N2.savehdf.in``) should be placed in the folder ``/mypsi4plugins/savehdf/``. The matrix elements can then be saved to disk in binary form with HDF5 by running:
.. code-block:: bash
$ cd /mypsi4plugins/savehdf
$ psi4 N2.savehdf.in N2.savehdf.out
$ ls *.h5
The plugin generates three files:
.. code-block:: bash
/mypsi4plugins/CheMPS2_Ham_parent.h5
/mypsi4plugins/CheMPS2_Ham_Tmat.h5
/mypsi4plugins/CheMPS2_Ham_Vmat.h5
which allow to create an instance of the ``CheMPS2::Hamiltonian`` object:
.. code-block:: c++
CheMPS2::Hamiltonian::Hamiltonian( const bool fileh5, const string main_file, const string file_tmat, const string file_vmat )
The variable ``fileh5`` should be ``true``, and the three strings should contain the paths to the three files listed above, in the same respective order.
.. _chemps2_psi4irrepconventions:
Custom matrix elements
----------------------
It is also possible to create a ``CheMPS2::Hamiltonian`` object with your own matrix elements. Please consult the ``CheMPS2::Hamiltonian`` class in the `doxygen html output <http://sebwouters.github.io/CheMPS2/doxygen/index.html>`_, and more specifically the functions:
.. code-block:: c++
CheMPS2::Hamiltonian::Hamiltonian( const int Norbitals, const int nGroup, const int * OrbIrreps )
void CheMPS2::Hamiltonian::setEconst( const double val )
void CheMPS2::Hamiltonian::setTmat( const int index1, const int index2, const double val )
void CheMPS2::Hamiltonian::setVmat( const int index1, const int index2, const int index3, const int index4, const double val )
The variable ``Norbitals`` should be the total number of orbitals in the active space. The variable ``nGroup`` should be the group number of the abelian point group with real-valued character table as defined in `psi4 <http://www.psicode.org/>`_. The array ``OrbIrreps`` of length ``Norbitals`` contains for each orbital its irreducible representation number as defined in `psi4 <http://www.psicode.org/>`_. The conversion table is provided here:
+----------------+-----+-----+-----+-----+-----+-----+-----+-----+
| Group / Irreps | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
+================+=====+=====+=====+=====+=====+=====+=====+=====+
| 0: c1 | A | | | | | | | |
+----------------+-----+-----+-----+-----+-----+-----+-----+-----+
| 1: ci | Ag | Au | | | | | | |
+----------------+-----+-----+-----+-----+-----+-----+-----+-----+
| 2: c2 | A | B | | | | | | |
+----------------+-----+-----+-----+-----+-----+-----+-----+-----+
| 3: cs | A' | A'' | | | | | | |
+----------------+-----+-----+-----+-----+-----+-----+-----+-----+
| 4: d2 | A | B1 | B2 | B3 | | | | |
+----------------+-----+-----+-----+-----+-----+-----+-----+-----+
| 5: c2v | A1 | A2 | B1 | B2 | | | | |
+----------------+-----+-----+-----+-----+-----+-----+-----+-----+
| 6: c2h | Ag | Bg | Au | Bu | | | | |
+----------------+-----+-----+-----+-----+-----+-----+-----+-----+
| 7: d2h | Ag | B1g | B2g | B3g | Au | B1u | B2u | B3u |
+----------------+-----+-----+-----+-----+-----+-----+-----+-----+
Two important remarks:
#. On creation of the ``CheMPS2::Hamiltonian`` object, every matrix element is set to zero.
#. Physics notation is used for the two-electron integrals in CheMPS2: :math:`V_{ij;kl} = ( ik \mid jl )` or ``CheMPS2::Hamiltonian::setVmat( i, j, k, l, (ik|jl) )``.
|