text: #!/usr/bin/env python
  # Copyright 2014-2019 The PySCF Developers. All Rights Reserved.
  #
  # Licensed under the Apache License, Version 2.0 (the "License");
  # you may not use this file except in compliance with the License.
  # You may obtain a copy of the License at
  #
  #     http://www.apache.org/licenses/LICENSE-2.0
  #
  # Unless required by applicable law or agreed to in writing, software
  # distributed under the License is distributed on an "AS IS" BASIS,
  # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  # See the License for the specific language governing permissions and
  # limitations under the License.
  #
  # Author: Qiming Sun <osirpt.sun@gmail.com>
  #
  
  '''
  Non-relativistic ROKS analytical nuclear gradients
  '''
  
  from pyscf import lib
  from pyscf.scf import addons
  from pyscf.grad import uks as uks_grad
  
  
  class Gradients(uks_grad.Gradients):
      '''Non-relativistic ROHF gradients
      '''
      def __init__(self, mf):
          uks_grad.Gradients.__init__(self, addons.convert_to_uhf(mf))
  
  Grad = Gradients
  
  from pyscf import dft
  dft.roks.ROKS.Gradients = dft.rks_symm.ROKS.Gradients = lib.class_as_method(Gradients)
  
  if __name__ == '__main__':
      from pyscf import gto
      from pyscf import dft
  
      mol = gto.Mole()
      mol.atom = [
          ['O' , (0. , 0.     , 0.)],
          [1   , (0. , -0.757 , 0.587)],
          [1   , (0. ,  0.757 , 0.587)] ]
      mol.basis = '631g'
      mol.charge = 1
      mol.spin = 1
      mol.build()
      mf = dft.ROKS(mol)
      mf.conv_tol = 1e-12
      #mf.grids.atom_grid = (20,86)
      e0 = mf.scf()
      g = mf.Gradients()
      print(g.kernel())
  #[[ -4.20040265e-16  -6.59462771e-16   2.10150467e-02]
  # [  1.42178271e-16   2.81979579e-02  -1.05137653e-02]
  # [  6.34069238e-17  -2.81979579e-02  -1.05137653e-02]]
      g.grid_response = True
      print(g.kernel())
  
      mf.xc = 'b88,p86'
      e0 = mf.scf()
      g = Gradients(mf)
      print(g.kernel())
  #[[ -8.20194970e-16  -2.04319288e-15   2.44405835e-02]
  # [  4.36709255e-18   2.73690416e-02  -1.22232039e-02]
  # [  3.44483899e-17  -2.73690416e-02  -1.22232039e-02]]
      g.grid_response = True
      print(g.kernel())
  
      mf.xc = 'b3lypg'
      e0 = mf.scf()
      g = Gradients(mf)
      print(g.kernel())
  #[[ -3.59411142e-16  -2.68753987e-16   1.21557501e-02]
  # [  4.04977877e-17   2.11112794e-02  -6.08181640e-03]
  # [  1.52600378e-16  -2.11112794e-02  -6.08181640e-03]]
  
  
      mol = gto.Mole()
      mol.atom = [
          ['H' , (0. , 0. , 1.804)],
          ['F' , (0. , 0. , 0.   )], ]
      mol.unit = 'B'
      mol.basis = '631g'
      mol.charge = -1
      mol.spin = 1
      mol.build()
  
      mf = dft.ROKS(mol)
      mf.conv_tol = 1e-14
      mf.kernel()
      print(Gradients(mf).kernel())
  # sum over z direction non-zero, due to meshgrid response
  #[[ 0  0  -2.68934738e-03]
  # [ 0  0   2.69333577e-03]]
      mf = dft.ROKS(mol)
      mf.grids.prune = None
      mf.grids.level = 6
      mf.conv_tol = 1e-14
      mf.kernel()
      print(Gradients(mf).kernel())
  #[[ 0  0  -2.68931547e-03]
  # [ 0  0   2.68911282e-03]]
  
  