ERKALE
ERKALE - DFT from Hel
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ERKALE is a code for Hartree-Fock and density-functional theory calculations for atoms and molecules. It uses a Gaussian basis set for representing the molecular orbitals and the electron density.
ERKALE is written in C++ and uses the Armadillo template library for linear algebra operations.
ERKALE is designed to be as easily maintained and user friendly as possible, but also to try to be reasonably fast.
I wanted to do some research on the modeling of inelastic x-ray scattering. This would require low-level access to a quantum chemical code.
The code would need to have a gentle learning curve, be reasonably fast for "production" use - and be free, so that I and others could use the code anywhere they liked.
As I did not find suitable existing programs on the market, I decided to write my own program. This would mean spending more time in development, although with the benefit of getting to grips with low level stuff. The decision was made a lot simpler due to the availability of fast, free libraries for computing electron repulsion integrals (libint) and exchange-correlation functionals (libxc), which meant that most of the dull stuff was already done by others.
Being free is also important because scientific results need to be reproducible. The path from equations to results is often very long in computational science; a working code used to implement the equations is (at least!) as important as the equations or the algorithms themselves. To guarantee that the code stays available, I have chosen the GNU General public license, which is commonly used in other scientific software as well.