  Mercury Fulminate (MF) is one of the well-known primary explosives since 17th
century and it has rendered invaluable service over many years. However, the
correct molecular and crystal structures are determined recently after 300
years of its discovery. In the present study, we report pressure dependent
structural, elastic, electronic and optical properties of MF. Non-local
correction methods have been employed to capture the weak van der Waals
interactions in layered and molecular energetic MF. Among the non-local
correction methods tested, optB88-vdW method works well for the investigated
compound. The obtained equilibrium bulk modulus reveals that MF is softer than
the well known primary explosives Silver Fulminate (SF), silver azide and lead
azide. MF exhibits anisotropic compressibility (b>a>c) under pressure,
consequently the corresponding elastic moduli decrease in the following order:
C22>C11>C33. The structural and mechanical properties suggest that MF is more
sensitive to detonate along c-axis (similar to RDX) due to high compressibility
of Hg...O non-bonded interactions along that axis. Electronic structure and
optical properties were calculated including spin-orbit (SO) interactions using
full potential linearized augmented plane wave method within recently developed
Tran-Blaha modified Becke-Johnson (TB-mBJ) potential. The calculated TB-mBJ
electronic structures of SF and MF show that these compounds are indirect
bandgap insulators. Also, SO coupling is found to be more pronounced for 4d and
5d-states of Ag and Hg atoms of SF and MF, respectively. Partial density of
states and electron charge density maps were used to describe the nature of
chemical bonding. Ag-C bond is more directional than Hg-C bond which makes SF
to be more unstable than MF. The effect of SO coupling on optical properties
has also been studied and found to be significant for both of the compounds.
