NOTE: routines in qmd_main are from the old routines called via nwmd. 
Not used in current qmd module

== QMD TODO items ==

* Applying constraints (Rattle, Shake)
* Simulated annealing
* CPMD style dynamics
* Metadynamics

=== rough flow-chart ==
r: coordinates
g: forces
v:
m:

qmd_init
*qmd_ext_init
qmd_coords_vel(r,v,m)

qmd_gradient(g) -> * qmd_ext_gradient(r,g)

do istep_nucl =

  qmd_nucl_vel(m,v,g)  ! v update at dt/2

  qmd_nucl_post(m,r,v) ! r update at dt

  qmd_gradient(g)

  qmd_nucl_vel(m,v,g)  ! v update at dt/2

enddo

PLUMED Interface
=========
F=-gradient . Need to invert sign



