Caesar; a utility for calculating the vibrational free energy of periodic crystals¶
Caesar calculates the vibrational free energy, and a number of related vibrational properties, of periodic crystals.
Purpose of Module¶
Caesar is intended to provide a vibrational method which is more accurate than the widely-used harmonic approximation [Hoja_ea] and the more sophisticated effective harmonic approximation [Errea_ea], but which is computationally inexpensive enough to be integrated into high-throughput workflows.
Caesar can calculate vibrational properties using several vibrational methods. The Caesar Harmonic Calculation Library performs calculations under the harmonic approximation [Hoja_ea]. The Caesar Anharmonic Calculation Library performs calculations under the vibrational self-consistent harmonic approximation (VSCHA) [Errea_ea] or using vibrational self-consistent field theory (VSCF) [Christiansen].
In order to perform vibrational calculations, Caesar must interface with an electronic structure code. A wide range of electronic structure codes can be used, via the Caesar electronic structure interface.
| [Hoja_ea] | (1, 2) First-principles modelling of molecular crystals: structures and stabilities, temperature and pressure. https://doi.org/10.1002/wcms.1294 |
| [Errea_ea] | (1, 2) Anharmonic free energies and phonon dispersions from the stochastic self-consistent harmomic approximation: Application to platinum and palladium hydrides. https://doi.org/10.1103/PhysRevB.89.064302 |
| [Christiansen] | Vibrational structure theory: new vibrational wave function methods for calculation of anharmonic vibrational energies and vibrational contributions to molecular properties. https://doi.org/10.1039/B618764A |
Building and Testing¶
The details of how to build and testing Caesar are given in the Caesar README.txt file.
Details of how the documentation and unit tests were written are presented in Caesar - Documentation and Testing.
Compilation¶
An out-of-source build is recommended. For this, a clean build directory should
be made, and then CMake and
Make should be run from the
build directory, e.g. as
mkdir build
cd build
cmake [options] path_to_src
make
where [options] are the desired CMake
configuration options, and path_to_src is the path to the caesar/src directory.
Caesar has been tested using version 10.1 of the gfortran compiler.
Dependencies¶
Caesar requires the spglib crystal symmetry
library. CMake will search LIB
for spglib’s lib directory, and will search
PATH for spglib’s include directory.
Caesar also requires the BLAS and LAPACK linear algebra libraries. These are located using CMake’s FindLAPACK utility, which searches a range of standard install locations and can be configured using additional CMake configuration options.
These dependencies can be suppressed by setting the
CMake options LINK_TO_SPGLIB and
LINK_TO_LAPACK to false, although this will disable many of Caesar’s features.
Documentation and Helptext¶
The software documentation for Caesar can be generated using
Ford. This should be generated in
the doc directory, by calling
ford caesar.md
Documentation will be generated in the doc/ford directory, and
doc/ford/index.html can be viewed by using an html reader (e.g. a web browser).
Caesar also has its own helptext system, which can be accessed through the
caesar executable by calling caesar --help. This system includes helptext for
each of the modes in which Caesar can be called, including details of the input settings
for each mode.
Unit Tests¶
The unit tests for Caesar are generated using
pFUnit. When building with
tests, pFUnit becomes a
dependency of Caesar, and CMake will search
PATH for pFUnit’s
bin directory.
Unit tests can be run by calling
ctest
from the build directory where CMake was run.
Unit tests are built by default, but can be suppressed by setting the
CMake option ENABLE_TESTS to false.
Output Visualisation¶
Caesar uses python scripts to visualise output data. These
can be run using Caesar, or can be run directly. When Caesar is built, the
python scripts will be written to the python directory
within the build directory.
Performing Calculations¶
Caesar is a command line utility. The behaviour of Caesar can be controlled using command line options, a configuration file, interactive input, or a combination of these. Detailed usage information can be obtained by calling
caesar --help
Source Code¶
The source code for Caesar is available from the Caesar repository