QMCPACK Examples

WARNING: TO RUN QUICKLY ENOUGH, MOST OF THESE EXAMPLES ARE NOT CONVERGED TO RESEARCH STANDARDS! YOU MUST CONVERGE PARAMETERS (STATISTICS, SIMULATION CELL SIZE, JASTROW PARAMETER NUMBER/CUTOFF, TWIST NUMBER, DMC TIME STEP, DFT PLANE WAVE CUTOFF, DFT K-POINT MESH, ETC.) FOR REAL CALCULATIONS!

The following examples should run on a modern workstation in a few hours.

Using QMCPACK directly

In examples/molecules are the following examples. Each directory also contains a README file with more details.

Directory

Description

H20

H2O molecule from GAMESS orbitals

He

Helium atom with simple wavefunctions

In examples/solid is a simple bulk solid LiH example, together with example Quantum ESPRESSO, PySCF, and RMG inputs to generate the orbitals. For research calculations on solids it is strongly encouraged to use Nexus for which many more examples are provided and e.g. twist averaging can be performed automatically.

Using Nexus

Extensive Nexus workflow examples are provided including (1) demonstrations of the use of Quantum ESPRESSO, PySCF, and Quantum Package to generate trial wavefunctions and perform subsequent QMC calculations, (2) application to isolated molecules and periodic systems with both plane-waves/splines and Gaussians, including periodic Gaussians, and (3) use of different estimators and analysis of the samples results.

For information about using Nexus, see the User Guide in nexus/docs or at https://nexus-workflows.readthedocs.io/ .

For Python to find the Nexus library, the PYTHONPATH environment variable should be set to <QMCPACK source>/nexus/lib. The executables for both QMCPACK and Quantum ESPRESSO (or relevant density functional or quantum chemical code) should be on the PATH, or the paths in the script should be adjusted.

These QMCPACK Nexus examples can be found under the nexus/examples/qmcpack directory.

Directory

Description

rsqmc_quantum_espresso/01_diamond_dft_vmc

Carbon diamond primitive cell, run with pseudopotentials and spline orbitabls from Quantum ESPRESSO, then VMC optimization with 1 and 2 body Jastrow factors.

rsqmc_quantum_espresso/02_diamond_dft_vmc_twistavg

As above, but including automatic generation of twist averaging over multiple twists.

rsqmc_quantum_espresso/03_diamond_dft_dmc_textrap

Carbon diamond example including generation of DMC runs for time-step extrapolation.

rsqmc_quantum_espresso/04_iron_dft_dmc_gcta

Full grand-canonical twist averaging (GCTA) example for bulk Fe including VMC with 1,2 and 3 body Jastrow factors and spin-density accumulation.

rsqmc_pyscf/01_h2o_hf_qmc

H\(_2\)O molecule, run all electron using Hartree-Fock orbitals from PySCF, then VMC optimization with 1,2 body Jastrow factors, then final DMC.

rsqmc_pyscf/02_diamond_hf_qmc

Periodic carbon diamond primitive cell, run with pseudopotentials and Quantum ESPRESSO, then VMC optimization with 1 and 2 body Jastrow factors, then final DMC.

rsqmc_quantum_package/01_h2o_hf_qmc

H\(_2\)O molecule, run all electron using Hartree-Fock orbitals from Quantum Package, then VMC optimization with 1,2 body Jastrow factors, then final DMC.

rsqmc_quantum_package/02_o2_selci_qmc

O\(_2\) molecule using 5000 determinants via configuration interaction, followed by QMC as above.

rsqmc_misc/H2O

H\(_2\)O molecule run with pseudopotentials and spline orbitabls from Quantum ESPRESSO, followed by VMC optimization and DMC.

rsqmc_misc/H2O_pyscf

H\(_2\)O molecule using PySCF. All electron then single VMC determinant only calculation.

rsqmc_misc/diamond

Carbon diamond supercell example including relaxation of atomic positions using Quantum ESPRESSO.

rsqmc_misc/diamond_pyscf

Carbon diamond primitive cell examples run with pseudopotentials and spline orbitals from Quantum ESPRESSO.

rsqmc_misc/diamond_radial_density

Spin density analysis example with computation of radial densities using qdens.

rsqmc_misc/diamond_lowdin

As above, but Lowdin analysis.

rsqmc_misc/oxygen_dimer

Binding curve for O\(_2\) molecule using pseudopotentials and spline orbitals from Quantum ESPRESSO.

rsqmc_misc/LiH

Bulk LiH primitive cell VMC and DMC example using BFD and CASINO format pseudopotentials and orbitals from Quantum ESPRESSO.

rsqmc_misc/excited

Excited state example for 16 atom supercell carbon diamond.

rsqmc_misc/O2_qp

O\(_2\) molecule using 5000 determinants via configuration interaction and Quantum Package, followed by QMC.

rsqmc_misc/estimators

Complete set of estimator specification examples applied for bulk Fe using DFT+U based orbitals.

rsqmc_misc/graphene

Graphene sheet DMC example including use of Nexus analyzer to obtain total energy.

rsqmc_misc/c20

C\(_{20}\) fullerene molecule using pseudopotentials and spline orbitals from Quantum ESPRESSO.