BLW

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BLW - must know

INPUT

The BLW input is that of Gamess supplemented by two groups to define the localization of the electrons.

$BLW group

BLW refers to the Block-Localized Wave function (BLW) method, which is a variant of the ab initio Valence Bond (VB) theory. This code can perform RBLW calculations for close-shell systems and ROBLW calculations for open-shell systems. It can also be combined with the grid-DFT calculations. The algorithm to derive self-consistent BLW is based on:

• 1) E. Gianinetti; M. Raimondi; E. Tornaghi, Int. J. Quant. Chem. 60, 157-166(1996).
• 2) A. Famulari, E. Gianinetti, M. Raimondi, M. Sironi, I. Vandoni, Theor. Chem. Acc. 99, 358-365(1998).
• 3) Y. Mo, S. D. Peyerimhoff, J. Chem. Phys. 109, 1687-1697 (1998).
• 4) Y. Mo, J. Gao, S. D. Peyerimhoff, J. Chem. Phys. 112, 5530-5538 (2000).
• 5) L. Song, Y. Lin, Y. Mo, J. Phys. Chem. A, 111, 8291-8301 (2007).

NBLOCK = number of blocks, the definition of each block shall be listed in $BLWDAT group. If nblock=1, it’s just a regular RHF/ROHF calculation.

ITER = maximum number of BLW cycles (default=50)

SCFCOV = NONE, do not take any actions during the SCF iterations DAMP, use damping of the Fock matrix if energy rises DIIS , selects Pulay's DIIS interpolation (based on FOCK matrix) DDIIS, selects Pulay's DIIS interpolation (based on density matrix) (default=DIIS)

IFZB(1) = an array that lists the blocks to be frozen (orbitals kept unchanged) during the optimization. This is useful to examine individual polarization effects, for example.

To switch DFT calculation to full accuracy since the very first step (for the guess orbitals), de-activate coarse grid . GAMESS starts DFT with coarse grid to accelerate the calculation. But if one needs to obtain the polarized energy, the energy of the first iteration shall be exact. To do so, add the following $DFT group. to the .inp file.

 $DFT NRAD0=96 NLEB0=302 NTHE0=12 NPHI0=24 $END

$BLWDAT group (required by $BLW)

For each block: NE NBF IFLAG

List of basis functions

NE is the number of electrons of that block. NBF is the number of basis functions of that block. IFLAG is an input control. IFLAG = 0, all the basis functions shall be specified; =1, the basis functions are sequential, and only the first one and the last one need be specified; =-1, this block has all the rest basis functions, thus no further specification.

The initial guess can be setup after the definitions of all blocks. It can be useful if the program fails to obtain convergence or one needs to derive the polarized energy term for the BLW-ED (energy decomposition) analysis. Note that the coefficients of MOs correspond to the list of basis functions in the definition lines of blocks. An blank line separates each blocks.

For example:
--------------------------------
$BLW  NBLOCK=2 $END
$BLWDAT
4 4 0       ← block 1 has 4 electrons and 4 basis functions
1 2 3 4    ← bfs of block 1
4 6 1    ← block 2 has 4 electrons and 6 basis functions
5 10     ← bfs of block 2 is from 5 to 10
1.0 0.0 0.0 0.0
0.0 1.0 0.0 0.0                ← initial guess for the 2 occupied orbitals(4/2) of block 1 
                             ← a blanck line at the end of the block
1.0 0.0 0.0 0.0 0.0 0.0   
0.0 1.0 0.0 0.0 0.0 0.0    ← initial guess for the 2 occupied orbitals(4/2) of block 2
$END
---------------------------------

Note: Eigenvalues and compositions of BLW-MOs are stored in $SCR/*.blw.

$BLWCI group

This part of code is intended to compute the coupling between two BLW’s which usually refer to the before- and after- charge transferred states in integral-direct way. References are:

• 1) Y. Mo, W. Wu, Q. Zhang, J. Chem. Phys. 119, 6448-6456 (2003).
• 2) Mo, Y., Song, L., Liu, M., Lin, Y., Cao, Z., Wu, W., J. Chem. Theory Comput., 8, 800-805 (2012).

BLWCI interaction between BLW structures

The figure illustrates the electronic coupling strength V_AB between two electron-localized states A and B as <math>\frac{1}{\sqrt{2}}</math>

NDET = the number of determinants NAEQB = 0, alpha and beta orbitals are not the same, so beta orbitals shall be inputted after alpha orbital

1, alpha and beta orbitals are the same, so only alpha orbitals will be inputted (default)

$BCIDAT group (required by $BLWCI) The coefficients of occupied MOs for each configuration shall be given here. occupied orbitals of 1st determinant occupied orbitals of 2nd determinant