  The refractive index of an optical medium is essential for studying a variety
of physical phenomena. One useful method for determining the refractive index
of scalar materials (i.e, materials which are characterized by a scalar
dielectric function) is to employ the Kramers-Kronig (K-K) relations. The K-K
method is particularly useful in cases where ellipsometric measurements are
unavailable, a situation that frequently occurs in many laboratories. Although
some packages can perform this calculation, they usually lack a graphical
interface and are complex to implement and use. Those deficiencies inhibits
their utilization by a plethora of researchers unfamiliar with programming
languages. To address the aforementioned gap, we have developed the Refractive
Index Calculator (RI-Calc) program that provides an intuitive and user-friendly
interface. The RI-Calc program allows users to input the absorption coefficient
spectrum and then easily calculate the complex refractive index and the complex
relative permittivity of a broad range of thin films, including of molecules,
polymers, blends, and perovskites. The program has been thoroughly tested,
taking into account the Lorentz oscillator model and experimental data from a
materials' refractive index database, demonstrating consistent outcomes. It is
compatible with Windows, Unix, and macOS operating systems. You can download
the RI-Calc binaries from our GitHub repository or conveniently access the
program through our dedicated web server at nanocalc.org.
