Example: Bond Energy analysis meta-GGA, (meta-)hybrids: Zn2, Cr2, CrH¶

#! /bin/sh


# This example illustrates the bond energy decomposition scheme using metaGGA or
# metahybrid or hybrid functionals in ADF.

# The first example is straightforward with closed shell atomic fragments: Zn_2.
# The second example has open shell atomic fragments: Cr_2, and the extra
# complication that spin symmetry breaking lowers the energy of the molecule,
# although the total S_z-value is zero. The third example has open shell atomic
# fragments, and the molecule is open shell: CrH.

# == Zn2 ==

# In the first example for Zn_2 the metahybrid TPSSh is used. In the bond energy
# analysis, the bond energy is split in a Pauli repulsion term, a steric
# interaction, and an orbital interaction.

AMS_JOBNAME=Zn2 $AMSBIN/ams <<eor
System
  atoms
     Zn 0.0 0.0 -1.6
     Zn 0.0 0.0  1.6
  end
end

Task SinglePoint

Engine ADF
  beckegrid
    quality good
  end
  basis
    core None
    type TZ2P
  end
  xc
    metahybrid TPSSh
  end
EndEngine

eor

# == Cr2 ==

# In the second example for Cr2 the metaGGA TPSS is used. You can use
# spin-unrestricted fragments in ADF. However, here simulated unrestricted
# fragments are used. A fair approximation to a computation with unrestricted
# fragments can be achieved with the key FRAGOCCUPATIONS. You tell ADF that you
# want to treat the fragments as if they were unrestricted; this causes the
# program to duplicate the one-electron orbitals of the fragment: one set for
# spin-alpha and one set for spin-beta. You can then specify occupation numbers
# for these spin-unrestricted fragments, and occupy spin-alpha orbitals
# differently from spin-beta orbitals. Especially for the Pauli-repulsion it is
# important that one chooses the spin-occupations on the different fragments
# such that they are 'prepared for bonding'.

# Of course, the unrestricted fragments that you use in this way, are not self-
# consistent: different numbers of spin-alpha and spin-beta electrons usually
# result in different spatial orbitals and different energy eigenvalues for
# spin-alpha and spin-beta when you go to self-consistency, while here you have
# spatially identical fragment orbitals. Nevertheless it is often a fair
# approximation which gives you a considerable extension of analysis
# possibilities.

# Spin-symmetry breaking is enforced by the use of the key ModifyStartPotential
# in combination with the key key UNRESTRICTED. In the ADF output one can find
# that there is spin-density on both of the atoms.


AMS_JOBNAME=Cr2 $AMSBIN/ams <<eor
System
  atoms
     Cr.1 0.0 0.0 -0.9
     Cr.2 0.0 0.0  0.9
  end
end

Task SinglePoint

Engine ADF
  beckegrid
    quality good
  end
  fragoccupations
     Cr.1
     S 4 // 3
     P 6 // 6
     D 5 // 0
     SubEnd
     Cr.2
     S 3 // 4
     P 6 // 6
     D 0 // 5
     SubEnd
  end
  modifystartpotential
     Cr.1 1 // 0
     Cr.2 0 // 1
  end
  basis
    core None
    type TZ2P
  end
  spinpolarization 0
  unrestricted
  xc
    metagga TPSS
  end
EndEngine

eor


# In order to calculate the effect of self-consistency one should calculate the
# Cr atom spin-unrestrictedly.


AMS_JOBNAME=Cr $AMSBIN/ams <<eor
System
  atoms
     Cr 0.0 0.0 0.0
  end
end

Task SinglePoint

Engine ADF
  beckegrid
    quality good
  end
  fragoccupations
     Cr
     S 4 // 3
     P 6 // 6
     D 5 // 0
     SubEnd
  end
  basis
    core None
    type TZ2P
  end
  spinpolarization 6
  unrestricted
  xc
    metagga TPSS
  end
EndEngine

eor


# == CrH ==

# In this example for CrH the hybrid B3LYP is used.

AMS_JOBNAME=CrH $AMSBIN/ams <<eor
System
  atoms
     Cr 0.0 0.0 0.0
     H  0.0 0.0 1.65
  end
end

Task SinglePoint

Engine ADF
  beckegrid
    quality good
  end
  fragoccupations
     Cr
     S 4 // 3
     P 6 // 6
     D 5 // 0
     SubEnd
     H
     S 0 // 1
     SubEnd
  end
  basis
    core None
    type TZ2P
  end
  spinpolarization 5
  unrestricted
  xc
    hybrid B3LYP
  end
EndEngine

eor


# In order to calculate the effect of self-consistency of spin-polarization on
# the atoms one should calculate the Cr and H atom spin-unrestrictedly.


AMS_JOBNAME=Cr_B3LYP $AMSBIN/ams <<eor
System
  atoms
     Cr 0.0 0.0 0.0
  end
end

Task SinglePoint

Engine ADF
  beckegrid
    quality good
  end
  fragoccupations
     Cr
     S 4 // 3
     P 6 // 6
     D 5 // 0
     SubEnd
  end
  basis
    core None
    type TZ2P
  end
  spinpolarization 6
  unrestricted
  xc
    hybrid B3LYP
  end
EndEngine

eor


AMS_JOBNAME=H $AMSBIN/ams <<eor
System
  atoms
     H 0.0 0.0 0.0
  end
end

Task SinglePoint

Engine ADF
  beckegrid
    quality good
  end
  fragoccupations
     H
     S 1 // 0
     SubEnd
  end
  basis
    core None
    type TZ2P
  end
  spinpolarization 1
  unrestricted
  xc
    hybrid B3LYP
  end
EndEngine

eor