4 Induced Current Density Programs 4.1 JBMAP - Current density vector map 4.3 STAGRA - Stagnation graph

4.2 BOCUST - Bond current strength

To obtain bond current strengths for each orientation of the perturbing magnetic fields, the program BOCUST can be used either interactively

prompt> BOCUST [ options ]

or redirecting the input from a file

prompt> BOCUST [ options ] < somefile.txt

The easiest way to use the program is to type the command without options. The program prompts for any pair of atoms found at a distance between the default values DISTMIN and DISTMAX. Replying y/Y the atom pair is selected for the current strength calculation, else the atom pair is skipped. Type N to exit immediately the calculation.
Sometime the list of atomic pairs could be relatively long. Therefore, preparing somefile.txt with one y/n per line could be useful in case to repeat the calculation with different options. In either case, a file BCS.3d is generated containing visual information about the calculated current strengths. It can be visualized using the v3d program 4.8.

The current strength CS is reported for each atomic pair in the output with the following format

 CONTRIBUTION  1 -0.5297042E+00 AU -0.1492675E-07 SI
 CONTRIBUTION  3  0.1773644E+00 AU  0.4998022E-08 SI
 TOTAL CS ==>    -0.3523398E+00 AU -0.9928726E-08 SI
 CS/CS0 ratio     0.83

where contributions are reported for each min/max of the current density cross section. The sum of contributions is given by TOTAL CS, which is the net bond current strength. Contributions and total are reported in atomic and SI units. The program uses a reference current strength CS0 (by default CS0=12 nA/T) and prints the ratio CS/CS0 after the TOTALE. The ratio $\times$ 100 is reported also on the graphic file. For a better comparison it is suggested to use the net bond current strength calculated for a benzene C-C bond using same method and basis set.

Defaults can be modified to consider particular cases using on-line command options. For a list of options type:

prompt> BOCUST -h
-o STRING graphic file name, do not add .3d
-f FAT molecular model scale factor
-g GX GY GZ gauge origin (a.u.)
-B BX BY BZ magnetic field components
-j TOT | ROT/PARA | TRA/DIA
-m CO|DZx|PZx|GRRO|GPRO|GRLN|CSGT|BS|BCP
-A GRRO/GPRO variable
-GRLN_N GRLN_N variable
-GRLN_Z GRLN_Z variable
-GCE STRING external grid file name
-q +-N O1 O2 ... ON: +add,-del MOs from the sum
-qf file reads +-N O1 O2 ...ON from file
-h this help
-----------------------
-p DELTA grid step (a.u.)
-x DIM OFFSET horizontal cross-section size (a.u.)
-y DIM OFFSET  vertical  cross-section size (a.u.)
-d DISTMIN minimum interatomic distance   (Ang)
-D DISTMAX maximum interatomic distance   (Ang)
-e VALORE contour level of integration domain (a.u.)
-emm VALORE min/max search criterion
-P FAT plot J as balls proportional to FAT
-C SPS plot line frame thickness proportional to SPS
-l 1,2,3,... progressive contour levels, if 999->3D
-I SPS ntegrate full frame, border line thickness=SPS
-CS0 REF reference current strength nA/T
-nocd dont plot points and domain contours

Up to -h, options are the same as for the JBMAP program 4.1. In particular the CTOCD details are described in 4.12.
Other options can be used to change: the grid grain (-p), the cross section rectangular size and its offset respect to the atomic pair center (-x, -y); the min and max distance between atoms to select atomic pairs (-d, -D); the value of the contour level which is used as integration domain (-e); the integration domain from contour levels to the full cross section (-I); the reference current strength (-CS0).

Examples for benzene, borazine and COT molecules are provided here in the following. Benzene computed at the same level of theory and basis set, has been chosen as a reference for all the molecules. Diatropic/paratropic circulations are clockwise/anticlockwise. At this level, borazine shows a sizable net diatropic ring current, whilst in COT the two C-C bond sustain a paratropic current which is nearly four times larger than the reference. The net current strengths for the X-H bonds is vanishing for benzene and borazine; for COT a very small current strength can be observed consistent with adjacent bay ring currents. Instructions and commands to generate the examples can be found here.