What is VB2000?

VB2000 is an ab initio electronic structure package for performing modern Valence Bond (VB) calculations based on a highly efficient VB algorithm—the so called Algebrant Algorithm. It has also a general implementation of the Group Function (GF) Theory, in which a large molecule is described in terms of its constituent parts of physically identifiable "electron groups".  The combination of the efficient VB algorithm and the general implementation GF theory in VB2000 makes it a useful tool for the investigation of the nature of chemical systems.

VB2000 is distributed in different packages for different platforms and third party systems. It can be used as a stand-alone program, which does not need a third party program for integrals and Hartree-Fock MO calculations. The stand-alone program can be installed on Unix/Linux platforms or on Microsoft Windows. The Windows version (WinVB2000) also has a simple graphic user interface. The Unix/Linux version can also be used as a plug-in module for GAMESS and Gaussian. The current release of Windows version of GAMESS (WinGAMESS) has VB2000 fully integrated and GAMESS provides an option to access VB2000 module.

• Integrated VB2000 into two major quantum chemistry programs, GAMESS(US) and Gaussian98/03 so that some of the functionalities of GAMESS and Gaussian can be used for VB wave function. Please note that you need the VB2000 package to upgrade GAMESS version July 5, 2005 (or later versions) or Gaussian 98/03.
  
• Introduced Valence Bond Orbital (VBO) Library files for construction of initial VB orbitals.
  
• Added graphic utilities for VB orbital visualization.
• Added maximum localization of VBOs of CASVB wave functions.
• Many technical enhancements: dynamic memory allocation, improved efficiency, enhanced the portability on many more platforms, added many more built-in basis sets.
  
• Improved the graphic user interface of  VB2000.NET for WinVB2000, the Windows version of VB2000 version 1.8. 
• Added structure weight analysis of Hiberty method.

Modern ab initio VB Method

VB2000 can be used for very general VB calculations:

• Multi-Structure VB (VB)
• Spin-Coupled VB (SCVB)
• Complete Active Space VB (CASVB)
• VB with Localized Electron Pairs (GVB)
• VB Configuration Interaction (VBCI)
  
• VB calcualtion with dynamic VB orbitals (BOVB type calculation).
  

Hartree-Fock Molecular Orbital Theory

Hartree-Fock molecular orbitals are generated before any type of VB calculations.  The HF orbitals are then used for generating an initial approximation to group functions and their corresponding initial one-electron densities.

Pipek-Mezey Localization Method

The Pipek-Mezey (PM) method for localization of molecular orbitals (MOs) has been implemented.

Group Function (GF) Theory

The general form of the GF theory has been fully implemented in VB2000. In general, a molecular wave function is expressed as an antisymmetrized product of individual group functions.The CASSCF and GVB type of wave functions are the special cases in the GF framework.

Structure Weight Analysis

Three methods for structure weight analysis have been implemented, i.e. the Mulliken type (i.e. the Chirgwin-Coulson type), the Lowdin type, and the Hiberty type.

Energy Profile of Chemical Reactions

VB2000 provides a functionality for the automatic calculation of the energy profile of a chemical reaction along the reaction path guided by a few intermediate structures (such as reactant, transition state, and product etc.).

Spin Density of VB Wave Functions

Spin density calculation has been introduced in VB2000 version 1.8(R2).

Visualization of VB Orbitals

Visualization files can be created so that VB oribtals can be visualized with third party programs, such as VMD and Molekel.
 

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Manual of VB2000 version 1.8(R2)   in PDF format

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