Example: Two-stage geometry optimization with initial Hessian¶

#!/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