# Custom Local Potential

Info

This file describes the contents of the kite/examples/custom_local_potential-folder.

This example shows how to use the custom local potential functionality in KITE.

Begin by defining the local energy function that you want to use. This is a function that takes as arguments the position ($$x$$, $$y$$) (in 2D) or ($$x$$, $$y$$, $$z$$) (in 3D) and orbital "orb" and returns the value of the local energy at that position and orbital. This function is defined by the user in a simple cpp file aux.cpp, which is then compiled into a shared library to be used by KITE libaux.so.1. To force KITE to use the function defined by the user, the file /lib/libaux.so.1 should be replaced by our custom shared library, and the flag custom_local=True must be used in the python configuration script. By default, this flag is set to False.

### 1. Compiling and replacing the default library¶

Begin by compiling the c++ file into a shared library by executing the following lines:

g++ -Wall -fPIC -c aux.cpp
g++ -shared -Wl,-soname,libaux.so.1 -o libaux.so aux.o


The first line compiles the aux.cpp file and the second generates the shared library from the compiled object. Next, replace the default shared library file in the /lib folder by the library that we just built

rm ../../lib/libaux.so.1
cp libaux.so ../../lib/libaux.so.1


The file libaux.so.1 is the file that KITE will search for. Now, the next time that KITE runs, it will use the library we just built.

### 2. Running the example¶

The rest proceeds as usual. Use python to generate the configuration file, run the KITE executable on that file and run KITE-tools on the same file again:

python config.py
../../build/KITEx config.h5
../../tools/build/KITE-tools config.h5


There is an extra flag in the configuration file custom_local_print=True, which tells KITE to generate the files local_potentialX.dat. By default, this flag is set to False. These files contain the potential as a function of position for all the lattice points used by KITE (one file per thread). These files can be further processed to generate a color plot of the potential for each orbital:

python3 test_potential.py


### 3. Finalizing¶

As a result of this whole process, the default shared library used by KITE in /lib has been changed. If the flag custom_local" is unspecified, or set to False, KITE will simply ignore this library, but if it is set to True, KITE will always use the shared library that was built in this example. It is recommended to simply not specify this flag, and KITE will have the intended behavior. If the user wants to restore the original library, a backup should be used, or the following three lines can be executed inside the /lib folder

g++ -Wall -fPIC -c aux.cpp
g++ -shared -Wl,-soname,libaux.so.1 -o libaux.so aux.o
ln -sf libaux.so libaux.so.1