  In this paper we describe a method to generate amorphous structures with
arbitrary structural constraints. This method employs the Simulated Annealing
algorithm to minimize a simple yet carefully tailored Cost Function (CF). The
Cost Function is composed of two parts: a simple harmonic approximation for the
energy-related terms and a cost that penalizes configurations that do not have
atoms in the desired coordinations. Using this approach, we generated a set of
amorphous carbon structures spawning nearly all the possible combinations of
$sp$, $sp^2$ and $sp^3$ hybridizations. The bulk moduli of this set of
amorphous carbons structures was calculated using Brenner's potential. The bulk
modulus strongly depends on the mean coordination, following a power law
behavior with an exponent $\nu=1.51 \pm 0.17$. A modified Cost Function that
segregates carbon with different hybridizations is also presented, and another
set of structures was generated. With this new set of amorphous materials, the
correlation between the bulk modulus and the mean coordination weakens. This
method proposed can be easily modified to explore the effects on physical
properties of the presence hydrogen, dangling bonds, and structural features
such as carbon rings.
