  A numerical parameter, referred to as a topological index, is used to
represent the molecular structure of a compound by analyzing its
graph-theoretical characteristics. Topological indices are predictive methods
for the physicochemical properties of chemical compounds in the context of
quantitative structure-activity relationship (QSAR) and quantitative
structure-property relationship (QSPR) analysis. Graph entropies have evolved
into information-theoretic tools for exploring the structural information of
molecular graphs. In this paper, we compute the Nirmala index, as well as the
first and second inverse Nirmala index, for the diamond structure using its
M-polynomial. Furthermore, entropy measures based on Nirmala indices are
derived for the diamond structure. The comparison of the Nirmala indices and
corresponding entropy measures is presented through numerical computation and
2D line plots. A regression model is built to investigate the relationship
between the Nirmala indices and corresponding entropy measures.
