Build instructions

Code structure

This package contains multiple components with varying interdependencies and dependencies on third-party libraries. You may not need to build all components, this depends on the intended use. The following table lists all components and their respective requirements (follow the links for more information).

Component	Requirements	Function
libnnp	C++11 compiler (icpc, g++)	NNP core library (NN, SF, Structure, …)
libnnpif	libnnp, MPI	Interfaces to other software (LAMMPS, …)
libnnptrain	libnnp, MPI, GSL, Eigen 3.3+	Dataset and training routines (Kalman, …).
nnp-convert	libnnp	Convert between structure file formats.
nnp-cutoff	libnnp	Test speed of different cutoff functions.
nnp-dist	libnnp	Calculate radial and angular distribution functions.
nnp-predict	libnnp	Predict energy and forces for one structure.
nnp-prune	libnnp	Prune symmetry functions.
nnp-select	libnnp	Select subset from data set.
nnp-symfunc	libnnp	Symmetry function shape from settings file.
nnp-atomenv	libnnptrain	Write atomic environment data to files.
nnp-checkdw	libnnptrain	Check analytic vs. numeric weight derivatives.
nnp-checkf	libnnptrain	Check analytic vs. numeric forces.
nnp-comp2	libnnptrain	Compare prediction of 2 NNPs for data set.
nnp-dataset	libnnptrain	Calculate energies and forces for a whole data set.
nnp-norm	libnnptrain	Calculate normalization factors for data set.
nnp-scaling	libnnptrain	Calculate symmetry function values for data set.
nnp-train	libnnptrain	Train a neural network potential.
lammps-hdnnp	libnnpif	Pair style `hdnnp` for LAMMPS
pynnp	libnnp, python, cython	Python interface to NNP library.
doc	Sphinx, Doxygen, Breathe	Documentation.

Dependencies

In order to compile n2p2 the following packages/libraries are needed

make

C++ Compiler (Makefiles are provided for GNU, Intel and LLVM)

Eigen

MPI Implementation (e.g. OpenMPI)

BLAS Implementation

GNU Scientific Library (GSL).

If the compiler can’t find Eigen although it is installed, you may need to create a symlink to the directory the compiler is looking for. This is explained here: https://eigen.tuxfamily.org/dox/GettingStarted.html.

For example on Ubuntu one can run

apt install build-essential libeigen3-dev libopenmpi-dev libblas-dev libgsl-dev

The master makefile

A master makefile is provided in the src directory which provides targets for all individual components. For instance, compiling the interface library libnnpif requires only to type

make libnnpif

in the src directory. Similarly, to build the application nnp-predict run

make nnp-predict

If an application depends on libraries, these will be built in advance automatically. Compiled binaries will be copied to the bin path (relative to the root directory), whereas libraries can be found in the lib folder. To clean up individual components use

make clean-<component>

or to clean everything (except documentation) use

make clean

By default, all libraries and applications will be built for static linking, i.e .a versions of libraries and statically built versions of executables are created. If dynamic linking is preferred use the MODE=shared switch as additional argument of the make command:

make MODE=shared nnp-predict

This will build .so versions of libraries and executables which require dynamic linking at runtime. Do not forget to point your linker to the lib directory, e.g. correctly set the environment variable LD_LIBRARY_PATH.

There are three different choices for the MODE switch:

static (default): This is the default which is used when no mode is explicitly set at the command line. Static build of libraries and applications.

shared: Use for dynamic linking, creates .so versions of libraries.

test: Special builds for CI tests and coverage reports.

Currently the build process has been tested with two different compilers, the GNU compiler g++ 5.4 (gnu) and the Intel compiler 17 (intel). It is possible to switch between them via the COMP variable, e.g.

make libnnp COMP=intel

If you need to change compiler variables and paths have a look at the corresponding makefiles containing global build parameters:

src/makefile.gnu
src/makefile.intel

You can also create new parameter makefiles based on the above and change the file name suffix according to your target:

src/makefile.<target>
make libnnp COMP=<target>

Note

In contrast to earlier versions it is now safe to use the -j switch to enable parallel compilation. By default only a single processor is used. For instance, in order to use 4 processors to build all components type:

make -j 4

Individual component makefiles

It is also possible to invoke individual makefiles for each component manually. Just switch to the corresponding folder and use make MODE=<mode> COMP=<target>. The global build parameters will be used from the src/makefile.<target> file.

Project-wide compilation options

Each of the build parameter makefiles src/makefile.<target> contains a section at the end which allows to enable/disable certain options at compile time:

Symmetry function groups

Flag: -DN2P2_NO_SF_GROUPS (default: disabled)

If this flag is set the symmetry function group feature will be disabled everywhere. This will result in a much worse performance but may be useful for debugging and development purposes. Note that disabling symmetry function groups will not change results, please see details in this publication [1].

Improved symmetry function derivative memory

Flag: -DN2P2_FULL_SFD_MEMORY (default: disabled)

By default n2p2 reduces the memory usage when multiple elements are present by eliminating storage for symmetry function derivatives which are zero by definition. This happens whenever a symmetry function is only sensitive to neighbors of certain (and not all) elements. Then, there is no space required for derivatives with respect to neighbors of all other elements and hence a significant amount of memory allocation can be avoided. The actual benefit depends on the symmetry function setup, as a rough estimate expect about 30 to 50% reduction. This feature is particularly useful for training of large data sets when symmetry function derivatives are stored in memory (keyword memorize_symfunc_results).

However, for debugging and development purposes (see e.g. this discussion) it can be helpful to keep the naive, full symmetry function derivative memory allocation. This can be achieved by enabling the flag -DN2P2_FULL_SFD_MEMORY. Only in this case there is a one-to-one correspondance between the list of symmetry functions in the libnnp output and the symmetry function derivative vectors in nnp::Atom::Neighbor::dGdr.

Normally, i.e. when -DN2P2_FULL_SFD_MEMORY is disabled, an additional section in the libnnp output will displayed after the SETUP: SYMMETRY FUNCTIONS section, which indicates the amount of still required memory for symmetry function derivatives. Here is how the output looks like for the RPBE-D3 water example (examples/nnp-predict/H2O_RPBE-D3):

*** SETUP: SYMMETRY FUNCTION MEMORY *******************************************

Symmetry function derivatives memory table for element  H :
-------------------------------------------------------------------------------
Relevant symmetry functions for neighbors with element:
-  H:   15 of   27 ( 55.6 %)
-  O:   19 of   27 ( 70.4 %)
-------------------------------------------------------------------------------
Symmetry function derivatives memory table for element  O :
-------------------------------------------------------------------------------
Relevant symmetry functions for neighbors with element:
-  H:   18 of   30 ( 60.0 %)
-  O:   16 of   30 ( 53.3 %)
-------------------------------------------------------------------------------
*******************************************************************************

Benchmarking the training program and the LAMMPS interface with the same system gives the following results:

`-DN2P2_FULL_SFD_MEMORY`	enabled	disabled	difference
Training (memory)	55.2 GB	37.8 GB	-31.5 %
MD with LAMMPS (memory)	725.6 MB	500.0 MB	-31.1 %
MD with LAMMPS (speed)	33.82 s	34.14 s	+0.9 %

Given the significant reduction in memory and the negligible impact on speed the improved memory layout is used by default (-DN2P2_FULL_SFD_MEMORY disabled).