Topic: static correlations, MCSCF, CASSCF

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Practice

• Static correlations in O2 molecule [O2]
  • Run RHF for singlet and check for stability
  • Correct the singlet by stable(opt) and look for spin contamination
  • Show that the triplet is ground state
  • Do CASSCF for singlet and triplet and analyze the wavefunction [Morrill1998] (use also RHF MOs to see orbital relaxation)
  • Do CASSCF for excited singlet and observe mor symmetric MOs for ground state singlet
  • Understand notations for molecular terms [Wikipedia]
  • Analyze results in terms of 2c2e UVX model
  • Compare state specific and state average CASSCF
  • Compare with XMCQDPT2 (accuracy vs time)
• Static correlations: Explain the electronic structure of the twisted ethylene and understand the rotation around C-C bond [ethylene]
  • Optimize geometry of twisted ethylene using CI method (OPEN(2,2) SINGLET SYMMETRY)
  • Is it a saddle point?
  • Explain the electronic structure
  • Compare with RHF and UHF calculations (single point) and explain the results (e.g. why UHF gives lower energy than CI)
  • Is there a spin contamination in UHF calculations?
  • Compare with C.I.=2 calculations and explain the difference
  • Look into nonsinglet states
  • Compare differences
  • Optimize geometry of planar ethylene using CI method (C.I.=2 SINGLET SYMMETRY)
  • Compare with OPEN(2,2) calculations (single point) and explain the difference
  • Compare rotation barrier for CI, RHF, and UHF
  • Rationalize bond lengths for planar and twisted conformations
  • Build relaxed PES for rotation imposing D2 symmetry
  • Build the same PES for triplet and excited singlet and discuss photoisomerization
  • Optimize geometry for triplet and excited singlet states
  • Compare S0 and S1 states at S1 geometry and discuss internal conversion
  • Look for NO occupancies in planar conformation (C.I.=7 AUX)
  • For planar conformation, which energy is a priori more accurate in semiempirical approaches RHF or CI?
• Static correlations in Li4 molecule [Li4]
  • Determine all states for which tetrahedral Li4 molecule is stable
  • Compare electronic structure of tetrahedral Li4 molecule with 4c4e tetrahedral model
  • Determine all states for which square Li4 molecule is stable
  • Compare electronic structure of square Li4 molecule with 4c4e square model
  • Determine the lowest energy conformer for each spin and charge state and calculate its energy relative to fully relaxed singlet
• Static correlations in transition metal complexes [Fe]
• Orbital relaxation: Explain Hund's rule [Oyamada2010]

Reading

• Jensen 4.6-4.7
• Cramer 7.2-7.4
• Szabo 4.5
• MOPAC manual: Open-shell configurations

Advanced level: transition metal coordination complexes

• Wikipedia: Coordination complex
• MOPAC manual: Transition metal complexes
• F Weinhold, C Landis, Valency and bonding: a natural bond orbital donor-acceptor perspective (CUP, 2005), chapter 4
• The Chemical Bond: Chemical Bonding Across the Periodic Table, ed G Frenking, S Shaik (Wiley, 2014), chapters 7,8
• I B Bersuker, Electronic Structure and Properties of Transition Metal Compounds: Introduction to the Theory (Wiley, 2010), 2ed
• T A Albright, J K Burdett, M-H Whangbo, Orbital interactions in chemistry (Wiley, 2013), 2ed, chapters 15,16