TURTLE Manual

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TURTLE

an ab initio VB/VBSCF program

by

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!
Extensions only applicable to the GAMESS version are indicated by underlining

Contents

Introduction

General Directives

SCF-directives


Introduction

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.
  • General Directives

    MFIL

    Currently under investigation.

    SFIL

    Currently under investigation.

    FFIL

    Currently under investigation.

    PASS

    Currently under investigation.

    ACCU

    Defines accuracy.

    ACTIVE

    Defines set of active orbitals. The number of active orbitals must exceed or equal the highest occupied orbital number. The active directive couples the orbitals defined with the CONF directive in CRESTR to the basis functions or a specified set of vectors. The active directive must be followed by 'end' Example:

    active
    1 2 5 6 7  
    end
    

    This statement couples the basisfunctions 1 2 5 6 and 7 to the functions 1 to 5 as defined in CRESTR.

    SPLICE / ONELEC

    Defines orbitals to be put in frozen core.

    VBVECTORS

    Tell TURTLE to read vectors from dumpfile or input.

    Syntax:

    vbvectors isec
    
    or 
    
    vbvectors manual n s [print]
    

    With isec the section of the dumpfile from wich the vectors are to be restored.

    Manual tells to read the vectors from input with n vectors to read and s columns to skip per row. Print is optional; when it is used the vectors will be printed in the output. After the line with vbvector the vectors have to be given.

    Example:

    vbvectors manual 4 1
    1  0.1000  0.3333 
    2  0.4444  0.1113
    3  0.0000  0.0005
    
    1  0.0000  0.0500
    2  0.0000  0.1000
    3  1.0000  0.6666
    

    SIZE

    Currently under investigation.

    BYPASS

    Currently under investigation.

    DIPOLE

    Currently under investigation.

    BLKSIZE

    Currently under investigation.

    CURTAIL

    Currently under investigation.

    TITLE

    The following line is read in as a title of the job.

    IPRINT

    Syntax:

    iprint i

    Sets printing level to i. Higher i yields more output.

    SHIFT

    Davidson shift.

    CRIT

    Davidson (and/or) jacobi stop-criterion (and/or) orthogonality criterion.

    MIX

    Mix input orbitals by hand.

    MAX

    Maximum number of cycles in davidson.

    CASES

    Analyse the types of matrix elements. Not fully implemented yet.

    SELECT

    States to select for starting vector.

    MODE

    Select diagonalisation mode.

    ALTER

    Level shift alteration in Davidson.

    MULLIKEN

    Atom definition in terms of orbital numbers. Defines which ao's belong to which atom and which basisfunctions belong to that atom. Directive must be followed by 'end'.

    Example:

    mulliken
     c1
     1 3 5 7 end
     1 to 12 end
     c2
     2 4 6 8 end
     13 to 24 end
    end
    

    HYBRIDS

    Try to make bonding hybrids according to rumer-bonds. The hybrids are guessed by maximising overlap.
    If this directive is followed by 'AO' then per atom the AO's will be used for it.

    CLEAR

    Clear ao's. That is remove coefficients on alien atoms. Atom definitions have to be given at the 'mulliken' option.

    NMOS

    Reduce the number of MO's defined in the active statement.

    SCHMIDT

    Orthogonalise vectors using Schmidt-orthogonalisation.

    LOWDIN

    Orthogonalise vectors using Lowdin-orthogonalisation.

    MOCOPY

    Copy MO's just read.

    ENERGY

    Read sum of atomic energies.

    EIGEN

    Request print of CI eigenvalues and eigenvectors.

    MRSD

    Currently under investigation.

    ENTER

    Input finished.

    SCF-directives

    SCF

    Start of SCF directives

     
       example:
    scf
    .....
    ....
    end 33 {scf}
    

    EXCIT / MIX

    Currently under investigation.

    CRIT

    Criterium for Jacobi, Davidson or SCF (default SCF).

    MAX

    Currently under investigation.

    MODE

    Currently under investigation.

    ALTER

    Currently under investigation.

    SHIFT

    Perform level shift in SCF.

    ORTHO

    The ortho directive allows one to switch off the allowed orthogonalisations; By default for instance singly occupied are orthogonalised to the doubly occupied ones. Note that the VBCI does not do these orthogonalitiations

        example :
          ortho off
    

    REMOVE

    Currently under investigation.

    HYBRID

    Define atoms for automatic atom-scf procedure.

    Syntax:

    hybrids
     atom 
     functions end
     basisfunctions end
    end
    

    Example:

    hybrids
     c1
     1 3 5 7 end
     1 to 12 end
     c2
     2 4 6 8 end
     13 to 24 end
    end
    

    FORCE

    Force orbitals to be equivalent.

    NOSYMM

    Do not use the symmetry.

    NOSPIN

    Do not use symmetry due to spin in matrix element evaluation.

    SUPER

    Do not allow internal excitations. These are replaced by excitations to ao's.

    FORBI

    Currently under investigation.

    PERT

    Treat excitations by perturbation theory.

      pert idelp itp shiftp
    

    start perturbation treatment of virtuals after del < idelp and iteration itp use a level shift of shiftp for the perturbation part.

    EVEC

    Optimize orbitals for excited state.

    References

    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)