The module fingerprint can be used for the computation of overlap matrix based fingerprints. The fingerprint vector contains the eigenvalues of the overlap matrix which is itself constructed from gaussian type orbitals. More detailed information can be found in [1] and [2]. The fingerprint can be calculated for periodic structures (src/fp_for_crystals.f90) or for clusters (src/fp_for_clusters.f90). For the calculation of non-periodic systems the lattice vectors (alat) have to be set to zero. For periodic systems the matrix alat contains columnwise the lattice vectors.

For all templates and modules the Makefile contains a compiling option DEBUG, where open-mp and all optimization flags are turned off for debugging the code. An example how this is used together with the intel you can find below:

make clean
make FC=ifort DEBUG=True
make fp_crystal FC=ifort DEBUG=True
cd build
./fp_crystal.x

The debug compiling flag is neither limited to the intel compiler nor to the template you are choosing to compile. By using the intel compiler, the lapack and blas operations are linked via the mkl library. If the gfortran compiler is used (default) it is linked to the standard lapack and blas libraries but it can also be linked to the ScaLAPACK and OpenBLAS library by using the following compiling flag:

make clean
make LAPACK=-lscalapack BLAS=-lopenblas
make fp_crystal LAPACK=-lscalapack BLAS=-lopenblas
cd build
./fp_crystal.x

The periodic version (src/fp_for_crystals.f90) is a template program to calculate the fingerprint of an Alanate crystal. If only the fingerprint without the derivative shall be calculated please set only_fp = .true., otherwise also the derivative of the fingerprint will be calculated and written into a file. Compiling this version can be done in the following way:

make clean
make
make fp_crystal
cd build
./fp_crystal.x

If you want to use the intel fortran compiler please use:

make clean
make FC=ifort
make fp_crystal FC=ifort
cd build
./fp_crystal.x

The cluster version (src/fp_for_clusters.f90) is a template program to calculate the fingerprint of a benzene molecule. The main difference in this version is that the unit cell vectors are set to zero. If only the fingerprint without the derivative shall be calculated please set only_fp = .true., otherwise also the derivative of the fingerprint will be calculated and written to files. Compiling this version can be done in the following way:

make clean
make
make fp_cluster
cd build
./fp_cluster.x

If you want to use the intel fortran compiler please use:

make clean
make FC=ifort
make fp_cluster FC=ifort
cd build
./fp_cluster.x

In this template program (src/fp_distance.f90) the fingerprint distance of two periodic perovskite crystals is calculated using the hungarian algorithm. The hungarian algorithm is taken from another GitHub repository and computes the translation, rotation and permutation of atoms that minimizes the RMSD between two crystalline configurations. Compiling this version can be done in the following way:

make clean
make 
make fp_distance
cd build
./fp_distance.x

If you want to use the intel fortran compiler please use:

make clean
make FC=ifort
make fp_distance FC=ifort
cd build
./fp_distance.x

There are two templates to test the fingerprint:

• Template for profing rotational invariance by rotating the system randomly
• Path integration of the derivative of the fingerprint to test its correctness.

Compiling and running the test for rotationial invariance can be done the following way:

make clean
make 
make test_invariance
cd build
./test_invariance.x

If you want to use the intel fortran compiler please use:

make clean
make FC=ifort
make test_invariance FC=ifort
cd build
./test_invariance.x

The result for the fingerprint distance should be zero, whereas the result of the scalar product of the coordinates is non zero.

Compiling and running the test for the fingerprint derivatives can be done the following way:

make clean
make 
make test_derivative
cd build
./test_derivative.x

If you want to use the intel fortran compiler please use:

make clean
make FC=ifort
make test_derivative FC=ifort
cd build
./test_derivative.x

The result is stored in the file Path_Integration.dat. The result can be visualized with gnuplot:

gnuplot plot_derivative.gnuplot

The output of the plotting is a png image (Path_Integraten.png). If the derivative is correct the two curves should nearly be the same with very small deviations. The deviations should get smaller the more integration steps are used (nint) in the src/test_derivative.f90 file.

With maximum volume simplex method [3] the fingerprint the vector length of the fingerprint can be compressed and brought to a unit length for machine learning purpuses. For the simplex compression two templates are aviable. The first template is using the simplex method to compress the fingerprint and also its derivative. The second template can be used for testing the derivative of the simplex compression.

This program is compressing the fingerprint to a unit length. If the variable only_fp = .true. only the fingerprint without the derivative is cumputed. Otherwise both, the fingerprint and its derivative are computed. Compiling and running the test for the fingerprint derivatives can be done the following way:

make clean
make 
make simplex
cd build
./simplex.x

If you want to use the intel fortran compiler please use:

make clean
make FC=ifort
make simplex FC=ifort
cd build
./simplex.x

After executing the program the file Correlation.dat is written which can be used to plot a correlation plot the following way:

gnuplot plot_correlation.gnuplot

In this template the derivative of the simplex compression is validated using a path integration. Compiling and running the test for the fingerprint derivatives can be done the following way:

make clean
make 
make test_simplex
cd build
./test_simplex.x

If you want to use the intel fortran compiler please use:

make clean
make FC=ifort
make test_simplex FC=ifort
cd build
./test_simplex.x

The result of the path integration can be plotted the follwing way:

gnuplot plot_derivative_simplex.gnuplot

Please cite the following articles if you use this code in an academic setting:

[1] Zhu, L. et al. (2016). A fingerprint based metric for measuring similarities of crystalline structures. J. Chem. Phys, 144(3)

[2] Sadeghi, A. et al. (2013). Metrics for measuring distances in configuration spaces. J. Chem. Phys, 139(18)

[3] Parsaeifard, B. et al. (2020). Maximum volume simplex method for automatic selection and classification of atomic environments and environment descriptor compression. J. Chem. Phys, 153(21)