**
VB2000, Version 2.7,
was released in 2013, and included in GAMESS(US) in 2014. Version 2.7
is still in the GAMESS(US) 2016 release, but version 2.8 is almost ready
for release. The purpose of this page is to collect
together everything we, the authors, and the VB2000 community have
learnt about using the program. Work of course is continuing on the
next release, and we will, at times, mention this. However, the main
thrust of this page is material that will help a user with the current version
version.
**

**We welcome items from users. Please e-mail them to Brian Duke**

** **

The following advice may help you to run VB2000 more effectively for your systems.

- If you want to run a multi-group VB calculation, specify the VB groups explicitly using the "dot" notation, such as VB(8).CASVB(6,6).VB(8). You can specify the same kind of calculation by using GPF(ng) and other controls, but the "dot" notation is much easier to use and intuitive.
- You can do a VB calculation of a molecule at one geometry and do another VB calculation on the same molecule at a different geometry by reading the VB orbitals of a previous calculation. This is not only a good way to speed up convergence of a new calculation, but also a necessary step for generating initial VB orbitals for a bond breaking calculation in some cases.
- If a VB group has many resonance structures and you have difficulty to determine which ones make major contributions, you can try a CASVB calculation first and then check the biggest contributors.
- Try to avoid running CASVB or SCVB for groups with large number of electrons (N>8 for CASVB and N>12 for SCVB - but SC(12,m) with m say 11 or 13 is more challenging). If you want to run SCVB(n) (n slightly larger than 12), you can try to run a VB(n) for orbital optimization with one or a few structures, and then do a SCVB(n) as a restart calculation without further optimization of VB orbitals (using key word CIONLY).
- The spin-density calculation can be very time consuming for group with more than 12 electrons.
- If VBSCF for VB orbital optimization becomes unstable, you can turn on DIIS. See Chapter 6 for more details about key word DIIS. The DIIS option helps to maintain the symmetry of wave function during VBSCF iterations.
- If the macro iteration is unstable (total energy becomes oscillating, you can set a damping factor for rigid rotation. See Chapter 6 for control $DAMPROT.

- All tests are using only one processor. The VB2000 codes do not support parallel processing.
- The Gamess/VB2000 version and the stand-alone version work fine with the gfortran and intel compilers.

We have used earlier versions VB2000 on Itanium 64 bit machine, on a SGI Irix, and on intel 64 bit processors with the Gamess TARGET=linux64 (using the g95 and pgf77 compilers). Thanks are due to Jörg Saßmannshausen, Institut für Chemische Technologie von Materialien. TU-Graz, Austria (now at University College, London) for allowing access to his machines for one of these tests.

We have tested both Gaussian03 and Gaussian09 on intel 64 bit processors at the Australian National Facility. Particular thanks are due to Rika Kobayashii, as Gaussian09 involves changes in the interface with VB2000. No such changes were involved in moving from Gaussian98 to Gaussian03. These Gaussian versions, where the VB2000 code is a separate Gaussian mode, is no longer supported.

From Gaussian09D1, where a large file of integrals and other value can be outout, there is a stand-alone VB2000 Gaussian version that reads that file. There is no longer the problem of compiling VB2000 into Gaussian when most uses do not have the source code.

- Using Gamess/VB2000 with the TRUDGE facility.
- Using Gamess/VB2000 with numerical gradients.

In case this is not clear from the Gamess/VB2000 test examples, the use of efffective core potentials is quite straight forward. Any potential that can be run with Gamess or Gaussian directly can be used with the Gamess/VB2000 combination.

Last updated: 10 December, 2016. Brian Salter-Duke (Brian Duke)