Linker IT Software
Google
Web www.oraxcel.com
menubar-top-links menubar-top-rechts
Home Help Search Login
Welcome, Guest. Please Login.
SQL*XL: Database to Excel bridge litLIB: Excel power functions pack ExcelLock: Locking and securing your valuable Excel spreadsheets encOffice: Protect your Excel file easy and safe encOffice: Protect your Excel file easy and safe
Pages: 1
Singlet and triplet instability of HF solutions (Read 1771 times)
Gerrit-Jan Linker
YaBB Administrator
*****




Posts: 75
Singlet and triplet instability of HF solutions
17.03.14 at 08:53:04
 
Singlet and triplet instability of HF solutions
 
Several solutions of the Hartree Fock (HF) equations may be close in energy. In restricted HF (RHF) we distinguish two types of instability of the RHF wavefunction
 
  • Singlet instabilities
    A RHF wavefunction has singlet instability when there is another solution with lower energy and a lower symmetry of the electron density. Such instabilities are indications for multi determinantal character. It shows as negative values on the diagonalised orbital hessian. The wavefunction is optimised to be intermediate between two lower solutions. It is optimised to a maximum.
     
  • Triplet instabilities
    A RHF wavefunction has triplet instability when the doubly occupancy of the MO's is rejected. This is the situation beyond the Coulson-Fisscher point where a UHF wavefunction yields a lower energy (compared to the RHF energy).  
     
    Source:
    IUPAC glossary of terms in theoretical organic chemistry
     
    References:
  • "Molecular Electronic Structure Theory", T. Helgaker, P. Jorgenssen, J. Olsen. Section 10.10 "Singlet and triplet instabilites in RHF theory"
  • M. M. Mestechkin. In Self-Consistent Field: Theory and Applications. (R. Carbo, A. Klobukowski, eds.) Elsevier, Amsterdam (1990).
  • K. Yamaguchi. Chem. Phys. 29, 117 (1978).
  • Back to top
     
    « Last Edit: 02.10.14 at 11:12:15 by Gerrit-Jan Linker »  

    Gerrit-Jan Linker
    Linker IT Software
    Email WWW Gerrit-Jan Linker   IP Logged
    Pages: 1