Purpose of Module

To obtain accurate results with ground state Quantum Monte Carlo methods (such as Variational and Diffusion Monte Carlo) an accurate trial wave function is essential. Such a wave function for an electron system will be typically given by the product of two factors: (1) a Jastrow term J describing electronic correlations and (2) a Slater determinant of suitable single particle orbitals \phi_i

\Psi({\bf R}) = J({\bf R}) \cdot \text{Det}(\phi_i({\bf r}_j))

where R is the vector containing the position of all electrons and r_i is the position of the i-th electron. While there is great freedom in the definition of the Jastrow term, that can then be variationally optimized, the single particle orbitals have to be computed in using Density Functional Theory.

The ESPWSCFInterface module provides a derived class of ESInterfaceBase to generate single particle orbitals for QMCPack via a DFT computation performed with Quantum Espresso.

Background Information

QMCPack is available from the github repository, and the documentation can be found in the QMCPack website

Quantum Espresso can be installed using the module QMCQEPack_qepatch, and the documentation can be found in the Quantum Espresso website

Building and testing

The ESPWSCFInterface module can be found in the QMCQEPack branch of the QMCPack git repository After cloning the repository and checking out the QMCQEPack branch with

git clone

git checkout QMCQEPack

one can proceed to download Quantum Espresso and build the library using the QMCQEPack_qepatch module.

Once the library is built one can proceed to build and compile QMCPack, as detailed in the official QMCPack documentation, or in the manual available in the manual subdirectory in the main QMCPack directory. Note that to use the Quantum Espresso interface the cmake options QE_INTERFACE must be used, typically with

cmake -DQE_INTERFACE=1 -DQMC_COMPLEX=1 <QMCPack base directory>

before compiling with make.

To use the interface one must use the qmcqepack keyword in the determinantset block in a QMCPack input file; further information can be found in Section 22.5.3 of the QMCPack manual, that can be compiled with the files in the manual directory.

The tests for this code are part of the deterministic unit tests for QMCPack, that can be run with the command

ctest -R interface

Note that the code is tested using the GCC compiler and OpenMPI.

Source Code

The source code is available available from in the QMCQEPack branch. Specifically relevant files for this module include:

  • src/Interfaces/PWSCF/ESPWSCFInterface.cpp
  • src/Interfaces/PWSCF/ESPWSCFInterface.h
  • src/Interfaces/PWSCF/pwinterface.h

and for the tests:

  • src/Interfaces/tests/
  • src/Interfaces/tests/test_interface_PWSCF.cpp