4 Induced Current Density Programs 4 Induced Current Density Programs 4.2 BOCUST - Bond current strength

4.1 JBMAP - Current density vector map

To obtain current density maps for each orientation of the perturbing magnetic fields, the program JBMAP can be used either interactively

prompt> JBMAP [ options ]

or redirecting the input from a file

prompt> JBMAP [ options ] < somefile.txt

The easiest way to use the program is to type the command without options and go forward accepting defaults. In this case, the (unitary) magnetic field is parallel to the $z$ Cartesian axis and the file JBF.3d is generated with the map to be visualized using the v3d program 4.8.

This could be enough in many a cases, in particular, for planar systems placed on the $x y$ plane. However, defaults can be modified to consider actual cases, using on-line command options and/or during the interactive use of the program. For a list of options type:

prompt> JBMAP -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

Most of these options depend on the flexibility of the CTOCD method and merit some attention. The -m option establishes the variant of the method, where some of them are more useful that others depending on the calculation type. However, it should be kept in mind that all CTOCD variants give the same result in the limit of a complete basis set calculation. For current density maps the default is DZ2, which is fine almost in all cases. For major details on -m, as well as on -g, -j, -A, -q, -qf options see 4.12.
The remaining options can be easily understood as discussed here below commenting the following command.

prompt> JBMAP -o map -f 0.1 -B 1 0 0 -GCE extgrid

In this example: the program generates the map.3d file with the graph of the current field; the thickness of the ball-and-stick molecular model is reduced to 0.1 respect to the default value of 0.3; the magnetic field is parallel to the $x$ Cartesian axis. It should be considered that even if the three components of $\mathbf{B}$ can be typed freely, the program always normalizes them to obtain a unitary perturbing field. The -CGE option permits to read an external grid of current density values from file extgrid. The extgrid text file contains Nato + NPoints lines. The first Nato lines have the format:

ΨAtomSymbol X Y Z

The NPoints lines have the format:

Ψx y z Jx Jy JzΨ

During the interactive use, the program prints:

------------------------------------------------------
FRE3D
magnetic field.........B    0.0000    0.0000    1.0000
gauge origin...........G    0.0000    0.0000    0.0000
comp 0=p+d,1=p,2=d.JTERM    0
method 0,1,2,3,4....METH    2
lower vertex..........RI   -6.0639   -6.6926   -2.0000
upper vertex..........RF    6.0639    6.6926    2.0000
cutoff min/max.......FMM    0.0200    0.1000
arrow fatt a0/J.....FATT    8.0000
arrow density.......STEP    0.6000
J.B>J*frac color....FRAC    1.0000
0=length,1=area.....LUNA    1
ok? [s]
------------------------------------------------------

and waits for some reply. The magnetic field components and the CTOCD details can be changed once again, but what matter here is the possibility to change the exploration space, as well as the cutoff filters, the arrow size and density. To make changes, type the proper key followed by a value, for example

 RI -6 -5 1
 RF  7  4 1
 FMM 0.05 1.5
 FATT 10
 STEP 0.4
 FRAC 0.3
 LUNA 0

These: to fix the exploration space to a plane at 1 au above and parallel to the $x y$ plane, extending from -6 to 7 au along $x$ and from -5 to 4 au along $y$ ; to set the cutoff filters to 0.05 and 1.5 au for the minimum and maximum current density vector module, respectively; to set a scale factor of 10 for the arrow size; to set a step of 0.4 au between grid points; to set to 0.3 the fraction of the current modulus along $\mathbf{B}$ to have arrow colors in red/blue if the fraction is parallel/anti-parallel to $\mathbf{B}$ . When LUNA is set to 0/1, arrow length/area is proportional to the modulus of the current density. When everything is ok, press the return key to complete the calculation. Collecting all these values in somefile.txt and redirecting the input from this file, is very useful to fix standard values to compare the maps of different molecules.

Examples of current density maps for benzene, borazine and planar cyclooctatetraene generated by JBMAP are shown in the following. Instructions and commands to calculate the maps here exposed can be found here.