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Predicting Molecular Properties  

2012-03-19 18:11:03|  分类: Gaussian |  标签: |举报 |字号 订阅

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The route section of a Gaussian 09 input file specifies the type of calculation to be performed. There are three key components to this specification:

  • The job type
  • The method
  • The basis set

The following table lists the job types available in Gaussian 09:

  • SP: Single point energy.
  • Opt: Geometry optimization.
  • Freq: Frequency and thermochemical analysis.
  • IRC: Reaction path following.
  • IRCMax: Find the maximum energy along a specific reaction path.
  • Scan: Potential energy surface scan.
  • Polar: Polarizabilities and hyperpolarizabilities.
  • ADMP and BOMD: Direct dynamics trajectory calculation.
  • Force: Compute forces on the nuclei.
  • Stable: Test wavefunction stability.
  • Volume: Compute molecular volume.
  • Density=Checkpoint Guess=Only: Recompute population analysis only.
  • Guess=Only: Print initial guess only; generate fragment-based initial guess.

In general, only one job type keyword should be specified. The exceptions to this rule are:

  • Polar and Opt may be combined with Freq. In the latter case, the geometry optimization is automatically followed by a frequency calculation at the optimized structure.

  • Opt may be combined with the compound method keywords in order to specify options for the optimization portion of the calculation: e.g., Opt=(TS,ReadFC) CBS-QB3.

When no job type keyword is specified within the route section, the default calculation type is usually a single point energy calculation (SP). However, a route section of the form: method2/basis2 // method1/basis1 may be used to request an optimization calculation (at method1/basis1) followed by a single point energy calculation (at method2/basis2) at the optimized geometry. For example, the following route section requests a B3LYP/6-31G(d) geometry optimization followed by a single point energy calculation using the CCSD/6-31G(d) model chemistry:

# CCSD/6-31G(d)//B3LYP/6-31G(d) Test

In this case, the Opt keyword is optional and is the default. Note that Opt Freq calculations may not use this syntax.

Predicting Molecular Properties

The following table provides a mapping between commonly-desired predicted quantities and the Gaussian 09 keywords that will produce them:

  • Antiferromagnetic coupling: Guess=Fragment, Stability
  • Atomic charges: Pop
  • ΔG of solvation: SCRF=SMD
  • Dipole moment: Pop
  • Electron affinities: CBS-QB3, CCSD, EPT
  • Electron density: cubegen
  • Electronic circular dichroism: CIS, TD, EOM, SAC-CI
  • Electrostatic potential: cubegen, Prop
  • Electrostatic potential-derived charges: Pop=Chelp, ChelpG or MK
  • Electronic transition band shape: Freq=FC, Freq=HT
  • Polarizabilities/hyperpolarizabilities: Freq, Polar [CPHF=RdFreq], Polar=DCSHG
  • High accuracy energies: CBS-QB3, G2, G3, G4, W1U, W1BD
  • Hyperfine coupling constants (anisotropic): Prop
  • Hyperfine spectra tensors (including g tensors): Freq=(VCD, VibRot [, Anharmonic])
  • Ionization potentials: CBS-QB3, CCSD, EPT
  • IR and Raman spectra: Freq[=Anharmonic]
  • Pre-resonance Raman spectra: Freq CPHF=RdFreq
  • Molecular orbitals: Pop=Regular
  • Multipole moments: Pop
  • NMR shielding and chemical shifts: NMR
  • NMR spin-spin coupling constants: NMR=Mixed
  • Optical rotations: Polar=OptRot
  • Raman optical activity: Freq=ROA, CPHF=RdFreq
  • Thermochemical analysis: Freq
  • UV/Visible spectra: CIS, ZIndo, TD, EOM, SAC-CI
  • Vibration-rotation coupling: Freq=VibRot
  • Vibrational circular dichroism: Freq=VCD
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