Example: Two-stage geometry optimization with initial Hessian
*************************************************************

"Download 2StepGO.run"

   #!/bin/sh

   # Preoptimization with DFTB and calculation of the Hessian
   # ========================================================
   #
   # We will reuse the geometry optimized at the DFTB level as a starting point for
   # the DFT geometry optimization. We will also calculate the real Hessian with
   # DFTB and use that as the initial Hessian for the Quasi-Newton based
   # optimization at the DFT level. DFTB is so fast compared to DFT, that all of
   # this is basically instantaneous. Our goal here is really just to reduce the
   # number of steps in the DFT geometry optimization. If we save just a single
   # step there, the initial DFTB calculation will already have paid for itself ...

   AMS_JOBNAME=dftb_preopt $AMSBIN/ams << EOF

      # Specify the system geometry: Aspirin
      System
          Atoms
              C         0.000000  0.000000  0.000000
              C         1.402231  0.000000  0.000000
              C         2.091015  1.220378  0.000000
              C         1.373539  2.425321  0.004387
              C        -0.034554  2.451759  0.016301
              C        -0.711248  1.213529  0.005497
              O        -0.709522  3.637718  0.019949
              C        -2.141910  1.166077 -0.004384
              O        -2.727881  2.161939 -0.690916
              C        -0.730162  4.530447  1.037168
              C        -0.066705  4.031914  2.307663
              H        -0.531323 -0.967191 -0.007490
              H         1.959047 -0.952181 -0.004252
              H         3.194073  1.231720 -0.005862
              H         1.933090  3.376356 -0.002746
              O        -2.795018  0.309504  0.548870
              H        -2.174822  2.832497 -1.125018
              O        -1.263773  5.613383  0.944221
              H        -0.337334  4.693941  3.161150
              H         1.041646  4.053111  2.214199
              H        -0.405932  3.005321  2.572927
          End
      End

      # Do a geometry optimization.
      Task GeometryOptimization

      # Also compute the Hessian at the optimized geometry.
      Properties
         Hessian True
      End

      # Settings for the DFTB engine:
      Engine DFTB
         Model DFTB3
         ResourcesDir DFTB.org/3ob-3-1
      EndEngine

   EOF


   # Geometry optimization with DFT
   # ==============================

   AMS_JOBNAME=dft_opt $AMSBIN/ams << EOF

      # Start from the geometry that is already optimized at the DFTB level.
      LoadSystem
         File dftb_preopt.results/dftb.rkf
      End
      # (equivalent to loading the system from dftb_preopt.results/ams.rkf)

      Task GeometryOptimization

      GeometryOptimization
         InitialHessian
            # Load the DFTB Hessian as the initial Hessian for the
            # Quasi-Newton based optimizer.
            Type FromFile
            File dftb_preopt.results
         End
      End

      # Settings for the BAND engine:
      Engine BAND
         Basis Type=TZP
         XC GGA=PBE
      EndEngine

   EOF
