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Note that using automatic guess works fine in a simple case like this one, using ''guess=mo'' simply accelerate convergence. However, for larger molecule, specifying a good orbital guess through ''guess=mo'' and an extra $gus section will often be useful.
 
Note that using automatic guess works fine in a simple case like this one, using ''guess=mo'' simply accelerate convergence. However, for larger molecule, specifying a good orbital guess through ''guess=mo'' and an extra $gus section will often be useful.
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For VBCISD calculation on difluorine : don't forget to add ''NCOR=2'' and ''ctol=0.01'' options in the ''$Ctrl'' section.
  
 
To compute the bond energies :
 
To compute the bond energies :
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* at the VBCISD level, you have to compute the separate fragments at this level of theory.
 
* at the VBCISD level, you have to compute the separate fragments at this level of theory.
  
Note that a more accurate BOVB bond energy could be obtained by pushing to [[The_SD_BOVB_method|higher SD-BOVB level]].  
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Note that a more accurate BOVB bond energy could be obtained by pushing to [[The_SD_BOVB_method|higher SD-BOVB level]], and with VBCISD by using a larger basis set.
 
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Version du 11 juillet 2012 à 15:35

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Basics of VB theory and XMVB program