********
Features
********

A primary motivation of pi-qmc is to have a framework so that features
developed by one student or for one research project can be used
in many different contexts.
Some of the many features developed for pi-qmc include:

* Bosons
* Exact fermions
* Fixed-node fermions
* Coulomb Interactions
* Linear Response Theory
* Electron-Hole recombination rates.
* Exact magnetic fields and fixed-phase.
* Multilevel sampling.
* Collective sampling.
* Free-energy sampling.
* Spin flips.

We are developing system integration tests to document and verify the status
of these features.

Applications
============

.. index:: molecules

Small Molecules
---------------
We have performed careful calculations on a H\ :sub:`2` molecule.


.. figure:: images/h2story.*
   :width: 100 %

   An illustrative calculation of a hydrogen molecule at 295 K.
   *(Top center)* A typical path in imaginary time for HD, showing low-mass 
   electrons (faint lines), a proton (blue, left) and a heavier 
   deuteron (black, right).
   *(Bottom center)* The same path, shown in real space.
   *(Top left)* Calculated bond length for H\ :sub:`2` and HD, showing 
   zero-point expansion from the *d* = 1.40 a\ :sub:`0` potential minimum and 
   thermal expansion due to molecular vibrations and rotations.
   *(Bottom left)* Dynamic fluctuations in the bond length give the 
   linear-response to a stretching force (inverse spring constant) and 
   vibrational frequency.
   *(Right side)* Fluctuations in the dipole give the polarizabilities α
   and hyperpolarizabilities γ.


.. index:: quantum dot


Quantum Dots
------------

.. index:: quantum point contact


Quantum Point Contacts
----------------------

Plasmas
-------

.. index:: Bose-Einstein condensate


Ultracold Atomic Gases
----------------------