  The fermionic molecular dynamics approach uses Gaussian wave packets as
single-particle basis states. Many-body basis states are Slater determinants
projected on parity, angular momentum and total linear momentum. The
wave-packet basis is very flexible - FMD contains harmonic oscillator shell
model and Brink-type cluster states as special cases. The parameters of the
wave packets are obtained by variation. A realistic effective interaction
derived from the Argonne V18 interaction by means of the unitary correlation
operator method is employed. We discuss the fully microscopic calculation of
the 3He(alpha,gamma)7Be capture reaction within the FMD approach. The model
space contains frozen cluster configurations at large distances and polarized
configurations in the interaction region. The polarized configurations are
essential for a successful description of the 7Be bound state properties and
for the S- and D-wave scattering states. The calculated cross section agrees
well with recent measurements regarding both the absolute normalization and the
energy dependence. We also discuss the structure of the cluster states,
including the famous Hoyle state, in 12C. From the two-body densities we
conclude that the Hoyle state has a spatially extended triangular alpha-cluster
structure, whereas the third 0+ state features a chain-like obtuse triangle
structure. We also calculate the N hbar Omega decomposition of our wave
functions to illuminate the challenges of no-core shell model calculations for
these cluster states.
