Installation Instructions

To build critic2, you will need:

These tools may already be available on your machine but, if they are not, they can be typically installed using a software package manager (apt, rpm, etc. on Linux; homebrew on macOS).

Build Using cmake

Using cmake is the recommended installation procedure, and the only way to build critic2 in recent versions. Change to the critic2 root directory and make a subdirectory for the compilation:

mkdir build
cd build

Then do:

cmake ..

There are a number of compilation options that can be passed to cmake, the most relevant of which is -DCMAKE_INSTALL_PREFIX=prefix, which sets the installation directory. You can tweak this and other compilation options using one of the multiple cmake interfaces, like ccmake (use ccmake .. from the build directory). To build the program, do:


You can use make -j n to use n cores for the compilation. Running make creates the critic2 binary in build/src/.

Some build options for advanced users: If you need to compile a static version of critic2, use:


The binary generated using this option can be copied to a different computer (with the same architecture), even if it does not have the compiler libraries, but you will need static versions of all the libraries (with extension .a) for the static build to work. To compile a version with debug flags,

cmake .. -DCMAKE_BUILD_TYPE=Debug

This version gives more informative errors when the program crashes, but it is slower.

Build Using configure/make

These instructions only apply to old versions of critic2; the configure/make build system has been removed from the development version. You need to run:


Prepare for compilation by doing:


Use configure --help for information about the different compilation options. The --prefix option to configure sets the installation path. More details about configure can be found in the INSTALL file included in the distribution. Once critic2 is configured, compile the program using:


This should create the critic2 executable inside the src/ subdirectory.

Installing and Setting up the Environment

Critic2 can be installed to the prefix directory by doing:

make install

However, the binary can be used directly from the source directory by setting the CRITIC_HOME environment variable. It must point to the root directory of the distribution:

export CRITIC_HOME=/home/alberto/programs/critic2

This variable is necessary for critic2 to find the atomic densities and other files. These files should be in ${CRITIC_HOME}/dat/.

Critic2 is parallelized with OpenMP for shared-memory architectures (unless disabled during compilation). You change the number of parallel threads by setting the OMP_NUM_THREADS environment variable.

Which Compilers Work?

Critic2 uses some features from the more modern Fortran standards, which may not be available in some older compilers. In consequence, not all compilers may be able to generate the binary and, even if they do, the binary may be broken. Two versions of critic2 are distributed. The development version, corresponding to the master branch of the repository, and the stable version, in the stable branch. Only patches addressing serious bugs will be introduced in the stable version; all new development happens in the development version. The stable version is compilable with all versions of gfortran starting at 4.9. All Intel fortran compiler versions from 2011 onwards also compile the stable code.

The development version can be compiled with gfortran-6 and later and with Intel fortran 2019 and later, although some recent versions of Intel fortran may cause problems if aggressive optimization is used. All other compilers tested have issues, and fail to produce a working binary. This is the list of compilers tested:

  • gfortran 4.8: critic2 cannot be compiled because allocatable components in user-defined types are not supported in this and older versions.
  • gfortran 4.9 through 5.4 (and possibly older and newer gfortran-5): the code compiles correctly but there are errors allocating and deallocating the global field array (sy%f) and other complex user-defined types. The program is usable, but problems will arise if more than one crystal structure or more than 10 scalar fields are loaded.
  • gfortran 6.x and above: no errors.
  • ifort, all versions from 12.1 up to 18.0.3: catastrophic internal compiler errors of unknown origin.
  • ifort, version 2019.0.3.199: it compiles but inexplicable segmentation faults with nonsensical tracebacks are thrown when using YT or BADER and when loading and unloading fields.
  • ifort, version 2019.0.5.281: if aggressive optimization is used (-O2 and -O3 flags), the compiler may freeze while compiling systemmod@proc.f90.
  • Portland Group Fortran compiler (pgfortran), version 17.3. There are two important compiler problems: i) passing subroutines and functions whose interface includes multidimensional arrays as arguments or function results does not work, and ii) internal compiler error when compiling meshmod.f90.

In summary: Only recent versions of gfortran and ifort are guaranteed to work with the development version. If you cannot use gfortran 6 or newer or ifort 2019 or newer, download the stable version. I do not think this is because of errors in the critic2 code (though if you find that it is, please let me know). If your compiler throws an internal compiler error while trying to build critic2, you may want to consider submitting a bug report to the compiler developers.

You can choose the compiler by setting the FC and CC environment variables to the path of your preferred compiler and then building in the usual way:

export FC=/usr/bin/gfortran-6 CC=/usr/bin/gcc-6
mkdir build
cd build
cmake ..

Once cmake generates the cache variables, the variables need not be set again, unless you delete the build directory.

External Libraries


When critic2 is built using cmake, it is possible to link against the readline library. This library enables shell-like features for critic2’s command line interface such as keyboard shortcuts, history, and autocompletion. You can typically find it in the repository of your chosen distribution.


Libxc is a library that implements exchange-correlation energies and potentials for many semilocal functionals (LDA, GGA and meta-GGA). In critic2, it is used to calculate exchange and correlation energy densities via de xc() arithmetic expressions (see below). Critic2 is not compatible with versions of libxc older than 5.0.

If you compile using cmake, libxc should be found automatically by the build system if it installed in a standard location. Otherwise, you can indicate the location of the include directory with the LIBXC_INCLUDE_DIRS variable and the location of the and with the LIBXC_xc_LIBRARY and LIBXC_xcf90_LIBRARY variables, respectively. For instance:

cmake -DLIBXC_INCLUDE_DIRS=/usr/include \
      -DLIBXC_xc_LIBRARY=/usr/lib/x86_64-linux-gnu/ \
      -DLIBXC_xcf90_LIBRARY=/usr/lib/x86_64-linux-gnu/ ..

The libxc library is used in critic2 to create new scalar fields from the exchange and correlation energy density definitions in the library using a density, gradient, or kinetic energy density already available to critic2 as a scalar field. For instance, if urea.rho.cube contains the electron density in the urea crystal, then:

CRYSTAL urea.rho.cube
LOAD urea.rho.cube
LOAD AS "xc($1,1)+xc($1,9)"

defines a scalar field (number 2, $2) as the LDA exchange-correlation density. In the output, the cell integral of the second field:

  Cell integral (grid SUM) = -23.30215685

is the LDA exchange-correlation energy in this system. GGA and meta-GGA exchange-correlation energy densities can be constructed in a similar way, but they require additional arguments to xc().

Another example: if we have a molecular wavefunction for benzene in benzene.wfx, we can build a field containing the PBE energy density and then integrate the PBE exchange-correlation energy with:

MOLECULE benzene.wfx
LOAD benzene.wfx
MOLCALC "xc($1,$1:g,101)+xc($1,$1:g,130)"

In this case, xc() takes two arguments: the density and the gradient. The :g field modifier is used to pass the gradient of the first field as the second argument to xc(). The MOLCALC keyword performs a numerical integration in a molecular mesh.

See the manual for more information.


Libcint is a library for calculating molecular integrals between Gaussian-Type Orbitals (GTOs). In critic2, this library is used mostly for testing but some options to the MOLCALC keyword and some functions in arithmetic expressions require it (e.g. the molecular electrostatic potential, mep).

To build critic2 with libcint support, you need to indicate the directory where the include directory (LIBCINT_INCLUDE_DIRS) and the location of the library file (LIBCINT_LIBRARY). For instance:

cmake -DLIBCINT_INCLUDE_DIRS=/home/alberto/git/libcint/build/include/ \
      -DLIBCINT_LIBRARY=/home/alberto/git/libcint/build/libcint.a ..

The libcint library is used with molecular wavefunctions that provide the basis set information. The mep(), uslater(), and nheff() chemical functions use the molecular integrals calculated by libcint, as well as the MOLCALC HF keyword. See the chemical functions and the MOLCALC sections of the manual.