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#! RHF cc-pVDZ energy for water, automatically scanning the symmetric stretch and bending coordinates
#! using Python's built-in loop mechanisms. The geometry is specified using a Z-matrix with variables
#! that are updated during the potential energy surface scan, and then the same procedure is performed
#! using polar coordinates, converted to Cartesian coordinates.
# Define the points on the potential energy surface using standard Python list functions
Rvals = [ 0.9, 1.0, 1.1 ]
Avals = range(102, 106, 2)
# Start with a potential energy scan in Z-matrix coordinates
molecule h2o {
O
H 1 R
H 1 R 2 A
}
count = 0
set basis cc-pvdz
set scf e_convergence = 11
set scf_type pk
for R in Rvals:
h2o.R = R
for A in Avals:
h2o.A = A
thisenergy = energy('scf')
count = count + 1
# And now the same thing, using Python's trigonometry functions, and Cartesian input. This time
# we want to reset the Cartesian positions every time the angles and bond lengths change, so we
# define the geometry inside the loops. N.B. this requires the basis set to be re-specified after
# every change of geometry
count = 0
for R in Rvals:
for A in Avals:
molecule h2o {
O 0.0 0.0 0.0
H 0.0 R 0.0
H 0.0 RCosA RSinA
}
# The non-numeric entries above just define placeholders with names. They still need
# to be set, which we do below.
h2o.R = R
h2o.RCosA = R * math.cos(math.radians(A))
h2o.RSinA = R * math.sin(math.radians(A))
set basis cc-pvdz
thisenergy = energy('scf')
count = count + 1