almaBTE consists of a library and a collection of executables allowing the user to calculate thermal transport properties of heterogeneous structures, using only ab-initio data, and solving the phonon Boltzmann Transport Equation (BTE).

Features of almaBTE 1.3 include

Supports a variety of material types

crystals
alloys
superlattices

Enables steady-state transport simulations in multiscale structures

bulk systems (thermal conductivity & capacity)
thin films (effective thermal conductivity)
multilayered structures (temperature profile, spectrally resolved heat flux, effective thermal conductivity)

Enables transient transport simulations in bulk systems

single pulse temperature response
mean square displacement of thermal energy

almaBTE includes all the capabilities of ShengBTE for single crystals (but in a fully new implementation with more efficient solution algorithms). almaBTE is fully written in C++ and freely distributed as open source under Apache 2.0 License.

Installing and compiling `almaBTE`

almaBTE relies on several external libraries (hdf5, boost and openMPI) that must be installed before compiling the main program. Detailed instructions for each supported operating system can be found below.

Installation on Ubuntu Linux

The following instructions have been tried on Ubuntu 16.10, freshly installed from the official AMD64 desktop image. They should be easily trasferable to other Debian-based distributions, and provide useful hints as to the required packages for other Linux systems.

1. Install CMake and the HDF5 and Boost libraries

From a terminal window, run this command:

sudo apt-get install cmake libboost-all-dev libhdf5-dev

You will be asked for your password. The system will then download and install all required dependencies.

2. Create a build directory

Move into the directory containing the almaBTE source code and run the following commands:

mkdir build
cd build
cmake ..

3. Compile `almaBTE`

From the build directory, run the following command:

make all

Note: you can speed up the process with parallel compilation. For example, if your CPU has 4 cores, you can use

make -j 4 all

4. Run the set of unit tests

almaBTE can run a series of test to check that the main modules work correctly on your system. To do so, run the following command from the build directory:

make test

5. Add the `almaBTE` executables to your `$PATH` so they can be run from any directory

Open ~/.bashrc in a text editor and add the following line:

export PATH=$PATH:"<alma_dir>/build/src"

where <alma_dir> must be replaced by the location of the main alma directory, for example /home/my_user/alma. After saving this change, reload the file with source ~/.bashrc or by opening a new shell.

Installation on macOS

almaBTE requires OS X Yosemite (10.10.5) or higher.

To begin the installation, open a Terminal window and perform the following steps.

1. Obtain `Xcode` command line tools

From the terminal window, type

xcode-select --install

A popup will appear, click Install and follow the graphic prompts.

2. Update the `Xcode` development environment

Obtain the current version of Xcode from the Mac App Store. You must have/create an Apple iTunes account to do so, but the download (about 4.5 GB, allow up to 2 hours) is free of charge. Xcode is required for correct functioning of Homebrew and proper compilation of almaBTE.

Once the download and installation are complete, open Xcode from the Applications folder. Accept the License Agreement, then close Xcode again.

3. Install the `Homebrew` package manager

Return to the Terminal window and type

ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"

4. Obtain `cmake` command line tools

brew install cmake

5. Obtain `HDF5` libraries

brew install homebrew/science/hdf5

6. Obtain `boost` and `openMPI` libraries

brew install boost --with-mpi

7. Compile `almaBTE`

Navigate to the alma main folder and execute the following

mkdir build
cd build
cmake .. -DCMAKE_BUILD_TYPE=RELEASE
make all

Note: you can speed up the process with parallel compilation. For example, if your CPU has 4 cores, you can use

make -j 4 all

8. Verify that `almaBTE` components function properly

Run the series of self-tests by executing

make test

9. Add the `almaBTE` executables to your `$PATH` so they can be run from any directory

sudo nano ~/.bash_profile

In the file, add the following line

export PATH="$PATH:<alma_dir>/build/src"

where <alma_dir> must be replaced by the location of the main alma directory, for example /Users/my_user_name/alma. Save the file using ctrl-O followed by enter, and close the editor with ctrl-X.

Finally, end the session by typing

exit

and close the Terminal window.

Main workflow of `almaBTE`

The workflow for performing thermal computations with almaBTE is graphically illustrated in the figure below (click for large version) and typically consists of the following two steps.

1. Obtain phonon properties of the materials of interest

In this step you will use VCAbuilder and/or superlattice_builder. These executables use ab-initio source files (downloadable from our online materials database) to determine the phonon dispersions, group velocities, and scattering matrix for three-phonon processes. The phonon properties are computed over a discrete wavevector grid with user-supplied resolution and stored in <material>.h5 files (hdf5 format). For superlattices, the file also contains the phonon scattering rates induced by mass disorder and barriers.

The hdf5 files only need to be created one single time for each material with a given grid resolution.

2. Solve the BTE for the structure of interest to extract thermal transport properties

For this step a variety of executables are available, each dedicated to perform specific simulations on bulk systems, thin films, and multilayer structures.

Thanks to the previously created hdf5 repository, phonon properties of the constituting compounds do not have to be recomputed but can simply be loaded from the files.

The structure geometry and computational settings are controlled by the user via xml input files.

Using `almaBTE`: Overview of each executable

Below follows a brief description of the executables.

Executables marked with [mpi] are parallellised; speed up execution by running them on multiple cores.

For a detailed illustration of the xml input syntax and generated outputs, please refer to the xml examples manual .

`VCAbuilder` [mpi]

VCAbuilder <inputfile.xml>

This executable builds hdf5 phonon property files for bulk materials.

Input

[Required] xml input file describing the desired material and grid resolution.

Several types of materials are supported:

<singlecrystal> (e.g. Si, GaAs, InAs, GaN, ...)
<alloy> (e.g. Si_0.5Ge_0.5, In_0.53Ga_0.47As, ...)
<parametricalloy> Automatic batch creation of alloy families (e.g. Si_1-xGe_x, In_xGa_1-xAs)

[Required] ab-initio source files downloadable from our online materials database

_metadata
POSCAR
FORCE_CONSTANTS
FORCE_CONSTANTS_3RD
BORN *(polar compounds only)*

Alloy creation requires ab-initio files for each constituting compound, for example generation of In_0.53Ga_0.47As needs files for InAs and GaAs.

Output

h5 file(s) for the specified material(s)

`superlattice_builder` [mpi]

superlattice_builder <inputfile.xml>

This executable builds hdf5 phonon property files for superlattices.

Input

[Required] xml input file describing the desired superlattice and grid resolution.

The superlattice is described in terms of its two consituting compounds, and the atomic concentration profile of a single period. (For details see the examples.)

[Required] ab-initio source files for the constituting compounds (see VCAbuilder).

Output

h5 file for the specified superlattice.

`phononinfo`

phononinfo <materialfile.h5> <OPTIONAL:Tambient>

This executable writes phonon information associated with a previously generated h5 file to a tabulated data file.

Input

[Required] Path to a previously generated h5 file for the material of interest.

[Optional] Ambient temperature. Set to 300K when omitted.

Output

Comma-separated data file (including a single-line header) with extension .phononinfo containing the following phonon properties:

q-point index nq [-]
branch index nbranch [-]
first wavevector coordinate qa [normalised to reciprocal lattice vector a]
second wavevector coordinate qb [normalised to reciprocal lattice vector b]
third wavevector coordinate qc [normalised to reciprocal lattice vector c]
angular frequency omega [rad/s]
volumetric heat capacity C [J/m^3-K] evaluated at the specified Tambient
lifetime tau [s] evaluated at the specified Tambient
x-component of group velocity vx [m/s]
y-component of group velocity vy [m/s]
z-component of group velocity vz [m/s]

`kappa_Tsweep`

kappa_Tsweep <inputfile.xml>

This executable computes the thermal conductivity tensor and volumetric heat capacity of bulk media as a function of ambient temperature.

Input

[Required] xml input file specifying the material of interest and desired temperature sweep.

[Required] previously generated h5 file for the material of interest

Output

csv file containing the thermal properties

`cumulativecurves`

cumulativecurves <inputfile.xml> <OPTIONAL:Tambient>

This executable computes the contribution of different phonons to bulk thermal conductivity and heat capacity at a given temperature.

Input

[Required] xml input file specifying the material of interest, thermal transport axis, and desired quantities.

The phonon contributions to thermal conductivity and capacity can be resolved by a variety of properties:

mean free path [m]
'projected' mean free path (MFP measured along the thermal transport axis) [m]
angular frequency [rad/ps]
frequency [THz]
energy [meV]
relaxation time [s]

[Required] previously generated h5 file for the material of interest

[Optional] Ambient temperature. Set to 300K when omitted.

Output

File(s) in csv format containing the requested cumulative quantities.

`kappa_crossplanefilms`

kappa_crossplanefilms <inputfile.xml> <OPTIONAL:Tambient>

This executable performs semi-analytic computation of the cross-plane apparent conductivity in thin films as a function of thickness at a given temperature. The program is also capable to provide a compact parametric fitting to the computed conductivity curve.

Input

[Required] xml input file specifying the material of interest, film orientation, and desired thickness sweep

[Required] previously generated h5 file for the material of interest

[Optional] Ambient temperature. Set to 300K when omitted.

Output

File in csv format containing the film conductivity, and optionally another csv file containing the parametric model parameters and curve.

`kappa_inplanefilms`

kappa_inplanefilms <inputfile.xml> <OPTIONAL:Tambient>

This executable performs semi-analytic computation of in-plane apparent conductivity in thin films as a function of thickness at a given temperature.

Input

[Required] xml input file specifying the material of interest, film orientation, and desired thickness sweep

[Required] previously generated h5 file for the material of interest

[Optional] Ambient temperature. Set to 300K when omitted.

Output

File in csv format containing the film conductivity

`steady_montecarlo1d` [mpi]

steady_montecarlo1d <inputfile.xml> <OPTIONAL:Tambient>

This executable performs variance-reduced Monte Carlo simulations of one-dimensional transport in thin films and multilayer structures embedded between two isothermal reservoirs.

Input

[Required] xml input file specifying the structure geometry, materials, and simulation settings

The following quantities will be computed by default:

temperature profile versus space
average heat flux, and its stochastic tolerance
system-wide effective thermal conductivity, and its stochastic tolerance
system-wide effective thermal resistivity and conductance

Upon user request, the program will also determine heat flux resolved by phonon frequency at user-specified locations.

[Required] previously generated h5 files for all materials present in the structure

[Optional] Ambient temperature. Set to 300K when omitted.

Output

csv file containing the computed temperature profile

txt file containing the thermal metrics

Optionally: csv files of spectrally resolved heat flux profiles

`steady_montecarlo1d_powersource` [mpi]

steady_montecarlo1d_powersource <inputfile.xml> <OPTIONAL:Tambient>

This executable performs variance-reduced Monte Carlo simulations of one-dimensional transport in thin films and multilayer structures with a planar power source at the top and ideal heat sink at the bottom.

Input

[Required] xml input file specifying the structure geometry, materials, and simulation settings

The following quantities will be computed by default:

temperature profile versus space
temperature rise at the heat source, and its stochastic tolerance
system-wide effective thermal conductivity, and its stochastic tolerance
system-wide effective thermal resistivity and conductance

Upon user request, the program will also determine heat flux resolved by phonon frequency at user-specified locations.

[Required] previously generated h5 files for all materials present in the structure

[Optional] Ambient temperature. Set to 300K when omitted.

Output

csv file containing the computed temperature profile

txt file containing the thermal metrics

Optionally: csv files of spectrally resolved heat flux profiles

`transient_analytic1d`

transient_analytic1d <inputfile.xml> <OPTIONAL:Tambient>

This executable computes semi-analytic solutions of the one-dimensional time-dependent BTE in bulk media at a given temperature.

Input

[Required] xml input file specifying the material of interest, the thermal transport axis, and the desired time sweeps.

Several quantities of interest can be computed:

single-pulse temperature profiles versus space at user-specified times
(only valid in weakly quasiballistic and diffusive regimes¹)
single-pulse temperature response at the heat source versus time
(only valid in weakly quasiballistic and diffusive regimes¹)
mean square displacement (MSD) of thermal energy versus time
(valid at all times, from fully ballistic to diffusive regimes)

¹ Time values must exceed characteristic phonon relaxation times.

[Required] previously generated h5 file for the material of interest

[Optional] Ambient temperature. Set to 300K when omitted.

Output

File(s) in csv format containing the requested transient solution(s)

Installing and compiling almaBTE

Installation on Ubuntu Linux

1. Install CMake and the HDF5 and Boost libraries

2. Create a build directory

3. Compile almaBTE

4. Run the set of unit tests

5. Add the almaBTE executables to your $PATH so they can be run from any directory

Installation on macOS

1. Obtain Xcode command line tools

2. Update the Xcode development environment

3. Install the Homebrew package manager

4. Obtain cmake command line tools

5. Obtain HDF5 libraries

6. Obtain boost and openMPI libraries

7. Compile almaBTE

8. Verify that almaBTE components function properly

9. Add the almaBTE executables to your $PATH so they can be run from any directory

Main workflow of almaBTE

1. Obtain phonon properties of the materials of interest

2. Solve the BTE for the structure of interest to extract thermal transport properties

Using almaBTE: Overview of each executable

VCAbuilder [mpi]

Input

Output

superlattice_builder [mpi]

Input

Output

phononinfo

Input

Output

kappa_Tsweep

Input

Output

cumulativecurves

Input

Output

kappa_crossplanefilms

Input

Output

kappa_inplanefilms

Input

Output

steady_montecarlo1d [mpi]

Input

Output

steady_montecarlo1d_powersource [mpi]

Input

Output

transient_analytic1d

Input

Output

Installing and compiling `almaBTE`

3. Compile `almaBTE`

5. Add the `almaBTE` executables to your `$PATH` so they can be run from any directory

1. Obtain `Xcode` command line tools

2. Update the `Xcode` development environment

3. Install the `Homebrew` package manager

4. Obtain `cmake` command line tools

5. Obtain `HDF5` libraries

6. Obtain `boost` and `openMPI` libraries

7. Compile `almaBTE`

8. Verify that `almaBTE` components function properly

9. Add the `almaBTE` executables to your `$PATH` so they can be run from any directory

Main workflow of `almaBTE`

Using `almaBTE`: Overview of each executable

`VCAbuilder` [mpi]

`superlattice_builder` [mpi]

`phononinfo`

`kappa_Tsweep`

`cumulativecurves`

`kappa_crossplanefilms`

`kappa_inplanefilms`

`steady_montecarlo1d` [mpi]

`steady_montecarlo1d_powersource` [mpi]

`transient_analytic1d`