NWChem

A simple SCF energy calculation on the input file start.xyz can be done with:

start en_scf
title "Pople SCF energy"

geometry units angstrom
  load start.xyz
end
basis
#   * library cc-pvdz
#   * library 6-31G*
   * library 3-21G
end

task scf energy

Running a geometry optimization just requires replacing the task directive. Here, we've also added a block of parameters controlling the minimization algorithm.

start opt_scf
title "Pople SCF geometry optimization"

geometry units angstrom
  load start.xyz
end
basis
#   * library cc-pvdz
#   * library 6-31G*
   * library 3-21G
end

driver
   loose
   maxiter 150
end
task scf optimize

You can also use DFT rather than HF (SCF) by changing the appropriate keywords and adding a DFT block to specify its functional:

start opt_dft

title "Pople DFT geometry optimization"

geometry units angstrom
  load start.xyz
end
basis
#  * library cc-pvdz
#  * library 6-31G*
  * library 3-21G
end
dft
  xc xpbe96 1.0 \
  pw91lda local 1.0 \
  cpbe96 nonlocal 1.0
  direct
  iterations 150
  grid fine
  disp vdw 2
end

driver
  loose
  maxiter 150
end
task dft optimize