----            ----         ----           ----   )))))
                      ----       ----         ----   _ _ _   { o o }
            ----                         ----      _(_)_(_)_  ( ^ )
     ----                   ----                 _(_)_(_)_(_)_/ /
----              ----                         _(_)_(_)_(_)_(_)/
                        ----                  (_)_(_)_(_)_(_)_(_)
 ----      ----                  ----           //  //   //  //


an ab initio VB/VBSCF program


J. Verbeek, J.H. Langenberg, C.P. Byrman, F. Dijkstra, J.J. Engelberts and J.H. van Lenthe

Utrecht (2001)

For comments mail to: Jeroen Engelberts : j.j.engelberts@chem.uu.nl

These pages are very much under construction!


TURTLE is a program designed to perform Valence Bond Self Consistent Field (VBSCF) calculations. The method used has been developed by Van Lenthe and Balint-Kurti. It has been implemented in the TURTLE package by Verbeek.

The wavefunction can be expressed in the following way:

Formule 1

The wavefunction is expressed as a linear combination of structures, the coefficients are variationally optimised.

The program has the following properties :

  • No restrictions are put on the number of configurations and structures.
  • Orbitals may be kept localised on atoms or fragments and may have single or double occupancy.
  • Both the orbitals and the coefficients of the structures are variationally optimised.
  • Analytical gradients are used to get insight into the structures of molecules and their reactions.
  • It has been made parallel to let it run on multiple processors at the same time.
  • It has been integrated into GAMESS-UK.
  • Structure

    The program has got the following structure: The links will lead you to the corresponding manuals.


    1. J.H. van Lenthe and G.G. Balint-Kurti, Chem Phys. Lett. 76, 138 (1980)
    2. J.H. van Lenthe and G.G. Balint-Kurti, J. Chem. Phys. 78, 5699 (1983)
    3. J. Verbeek, Nonorthogonal orbitals in ab initio many-electron wavefunctions, Ph.D. Thesis, Utrecht University (1990)
    4. C.P. Byrman, Nonorthogonal orbitals in Chemistry, Ph.D. Thesis, Utrecht University (1995)
    5. F. Dijkstra, Valence Bond theory, implementation and use of analytical gradients, Ph.D. Thesis, Utrecht University (2000)