1 Introduction

This guide covers the installation and usage of the thermo_pw package. It assumes that you have some familiarity with the QUANTUM ESPRESSO package. If not please consult the web site: http://www.quantum-espresso.org.

thermo_pw is a FORTRAN code that computes material properties. It can be thought as a set of drivers that, at low level, call the QUANTUM ESPRESSO routines and, at high level, have pre-processing tools to reduce the information provided by the user and post-processing tools to convert the output of QUANTUM ESPRESSO into plots of material properties directly comparable with experiment.

thermo_pw has the following directory structure, contained in a subdirectory thermo_pw/ that should be put in the main directory of the QUANTUM ESPRESSO tree:

Doc/	: contains this user's guide and other documentation
examples/	: some running examples
inputs/	: a collection of useful inputs
pseudo_test/	: a collection of inputs to test a pseudopotential library
space_groups/	: a collection of structures for many space groups
lib/	: source files for modules used by thermo_pw
src/	: source files for thermo_pw
tools/	: source files for auxiliary tools
tools_input/	: examples of inputs for the auxiliary tools

The thermo_pw package can calculate the following quantities:

• Plot of the Brillouin zone (the structure can be seen by reading the input of thermo_pw by the XCrySDen program).

• Plot of the X-rays powder diffraction pattern of the input crystal.

• Total energy at fixed geometry.

• Total energy as a function of the kinetic energy cut-off.

• Total energy as a function of k-points and smearing.

• Electronic band structure at fixed geometry.

• Electronic density of states at fixed geometry.

• Electronic heat capacity as a function of temperature (for metals only).

• Complex dielectric constant as a function of the complex frequency $\omega$ at fixed geometry.

• Inverse dielectric constant at a given wavevector q as a function of the complex frequency $\omega$ at fixed geometry.

• Phonon frequencies at fixed geometry.

• Phonon dispersions at fixed geometry and computation of the harmonic thermodynamic properties: vibrational energy, vibrational free energy, vibrational entropy, and constant volume heat capacity as a function of temperature.

• Frozen ions and relaxed ions elastic constants at fixed geometry.

• Fit of the total energy as a function of the lattice parameters with a quadratic or quartic polynomial and determination of equilibrium lattice parameters. Murnaghan fit.

• Electronic band structure at the minimum of the total energy.

• Electronic density of states at the minimum of the total energy.

• Complex dielectric constant as a function of the complex frequency $\omega$ at the minimum of the total energy.

• Inverse dielectric constant at a given wavevector q as a function of the complex frequency $\omega$ at the minimum of the total energy.

• Phonon frequencies at the minimum of the total energy.

• Phonon dispersions and harmonic thermodynamic quantities at the minimum of the total energy.

• Frozen ions and relaxed ions elastic constants at the minimum of the total energy.

• Anharmonic properties within the quasi-harmonic approximation: lattice parameters, thermal expansion tensor, volume, volume thermal expansion, and constant strain heat capacity as a function of temperature; phonon frequencies and mode Grüneisen parameters interpolated at a given geometry or at the equilibrium geometry at a given temperature (limited to cubic, tetragonal, orthorhombic, and hexagonal systems). Bulk modulus and pressure derivative of the bulk modulus, isobaric heat capacity, isoentropic bulk modulus, and average Grüneisen parameter as a function of temperature (limited to cubic systems). Minimum Helmholtz (or Gibbs at finite pressures) free energy as a function of temperature.

• Surface band structure identification and plot of the projected bulk band structure.

thermo_pw can run on both serial and parallel machines using all the parallellization options of QUANTUM ESPRESSO. Moreover, thermo_pw can run using several images. When possible, the image parallelization is used in an asynchronous way. One image takes the role of master and distributes the work to all the images that carry it out independently. Presently the total energies of several geometries for the determination of the equilibrium geometry are calculated in parallel when there are several images. Stresses or total energies at different strained geometries needed for the calculation of the elastic constants are calculated in parallel. The phonon calculations are carried out in parallel, each image doing one representation of a q point. For frequency dependent calculation, each frequency, or group of frequencies, can be calculated in parallel by different images.