Xiamen Valence Bond (XMVB) is a valence bond (VB) theory based quantum chemistry program for performing electronic structure calculations. It provides an elegant way to faithfully represent classical VB theory, in which Heitler-London-Slater-Pauling (HLSP) functions service as the state functions and nonorthogonal orbitals are utilized to build the many-electron wave function of molecule. Since 1986, the XMVB developers at Xiamen University have devoted their endeavors to revive the VB theory by continuingly enriching the package with novel methodologies and algorithms. We hope that XMVB would became an efficient tool for exploring the nature of chemical bond and contributing to the coming renaissance of VB theory.

Major events in XMVB development :

In 1989, a pilot VB code based on symmetric group approach (SGA) was accomplished and applied to H3 molecule.
In 1992, a novel algorithm based on the left coset decomposition of the symmetric group was proposed and implemented.
In 1995, the paired-permanent-determinant (PPD) approach was introduced to evaluate the Hamiltonian matrix efficiently, especially for systems comprising many covalent bonds.
In 1999, Xiamen-99, which is the precursor of XMVB code, was released.
In 2002, VBCI method was implemented.
In 2003, XMVB was named; and Version 1.0 was released.
In 2004, VBPCM method was available in XMVB.
In 2005, the parallel version of XMVB was released.
In 2008, a novel analytical gradients based orbital optimization scheme was proposed; and VBMM and VBSM methods were available in XMVB.
In 2009, VBPT2 method was implemented.
In 2010, the module distribution of XMVB was incorporate to the GAMESS-US package.
In 2011, DFVB and VBEFP methods were available in XMVB.
In 2012, the reduced density matrix based approach was developed.
In 2012, Version 2.0 was released.
In 2013, VBSCF(CAS) method was available in XMVB.
In 2014, the automatic formula and code generator (AFCG) was implemented.
In 2014, Version 2.1 was released.
In 2016, matrix element correction based DFVB was available in XMVB.