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 QMCQEPack_qepatch provides the files to properly patch Quantum Espresso 5.3 to build the libpwinterface.so library; this library is required to use the module ESPWSCFInterface to generate single particle orbitals during a QMCPack computation using Quantum Espresso.

Background Information

QMCPack is available from the github repository https://github.com/QMCPACK/qmcpack, and the documentation can be found in the QMCPack website https://qmcpack.org/documentation.

Quantum Espresso can be installed using this module, and the documentation can be found in the Quantum Espresso website https://www.quantum-espresso.org/resources/users-manual.

Building and testing

The QMCQEPack_qepatch module can be found in the QMCQEPack branch of the QMCPack git repository https://github.com/michruggeri/qmcpack/tree/QMCQEPack. After cloning the repository and checking out the QMCQEPack branch with

git clone https://github.com/michruggeri/qmcpack.git

git checkout QMCQEPack

one can proceed to build the libpwinterface.so library using the using the script QMCQEPack_download_and_patch_qe.sh in the external_codes/quantum_espresso directory. After patching the code one has to use the configure script in the resulting q-e-qe-5.3 directory and finally compile the libpwinterface.so library with make pw. Note that when building the code it may be required to use the internal Quantum Espresso version of the FFTW libraries. In order to do so if is sufficient to change in the DFLAGS field of the make.sys file generated by the configure script -D__FFTW3 with -D__FFTW.

To use this library to perform DFT simulations QMCPack must be suitably compiled; the relevant information can be found in the documentation of the ESPWSCFInterface module.

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 https://github.com/michruggeri/qmcpack/tree/QMCQEPack in the QMCQEPack branch. Specifically relevant files for this module include:

  • external_codes/quantum_espresso/QMCQEPack_qepatch.diff
  • external_codes/quantum_espresso/QMCQEPack_download_and_patch_qe.sh