The execution needs to be done in two steps.

(i) The first step is to execute ej_calc_form. If the input files are File1 and File2, then the following command can be used::

ej_calc_form File1 File2

It is necessary to run ej_calc_form to produce the singul file which is required to calculate the coupling constant using ej_calc_spin.

(ii) This is followed by the execution of ej_calc_spin as:

ej_calc_spin File1 File2

File1 contains the definition of the Hamiltonian.

File2 contains the value of spin operators for each paramagnetic centre and the energy of different spin states.

The details about the coupling constants are printed in the files File1_form.out and File1_spin.out for formal spins and spin densities respectively.

The details of the format for File1 and File2 are provided later in this section.

The execution of the suscep code requires three input files, and for input files named File1, File3 and File4, the suscep code can be executed in the following way:

suscep File1 File3 File4

File1 contains the definition of the Hamiltonian.

File3 contains the additional information other than the J-values required to calculate the temperature dependence of magnetic susceptibility.

File4 contains the magnitude of J-values to be used for the determination of magnetic susceptibility.

The temperature dependence of magnetic susceptibility is printed in the file File1.out.

The details of the format for the input files are provided later in this section.

For ease, a bash script (j2suscep) has also provided in the bin directory that can be used to execute the codes separately or together as described below:

The code ej_calc_spin can be executed using the '-s' tag for input files File1 and File2 as follows:

j2suscep -s File1 File2

The use of the '-s' tag leads to the execution of either ej_calc_spin (if a 'singul' file exists in the working directory), or both ej_calc_form and ej_calc_spin (if a 'singul' file does not exist in the working directory).

To execute the code ej_calc_form as a separate step, one can use the '-f' tag. For input files File1 and File2, the execution can be performed as follows:

j2suscep -f File1 File2

For input files File1, File3 and File4, the code suscep can be executed as follows:

j2suscep -S File1 File3 File4

Both the ej_calc and suscep codes can also be executed in one go. For this, again three files are required:

1. File1, which contains the details about the Hamiltonian.
2. File2, which contains information about the the value of spin operators for each paramagnetic centre and the energy of different spin states.
3. File3, which contains the additional information other than the J-values required to calculate the temperature dependence of magnetic susceptibility.

Although another file (File4) is generally required for the execution of the suscep code, a combined execution of both codes generates this file automatically. The execution is performed as follows:

j2suscep -a File1 File2 File3

The j-values determined using the ej_calc_spin codes are written to a file named 'jvals' and are used for the calculation of the temperature dependence of magnetic susceptibility.

The usage information for this script can also be accessed as follows:

j2suscep -h

The following information is displayed with the use of the -h tag:

***J2suscep help***
For executing ej_calc_spin:
j2suscep -s File1 File2
For executing ej_calc_form:
j2suscep -f File1 File2
For executing suscep:
j2suscep -S File1 File3 File4
For executing all codes together:
j2suscep -a File1 File2 File3
For help:
j2suscep -h
Information expected within different input files
File1 should contain the details about the Hamiltonian.
File2 should contain information about the the value of spin operators for each paramagnetic centre and the energy of different spin states.
File3 should contain the additional information other than the J-values required to calculate the temperature dependence of magnetic susceptibility.
File4 should contain the magnitude of J-values to be used for the determination of magnetic susceptibility.

File1 contains the definition of the Hamiltonian. The format of this file is as follows:

magnetic centres
<number of paramagnetic centres>
No. of J values
<number of j-value>
Hamiltonian
<First interaction associated with the first j-value>
<Second interaction associated with the first j-value>
<Third interaction associated with the first j-value>
And so on
****
<First interaction associated with the second j-value>
<Second interaction associated with the second j-value>
<Third interaction associated with the first j-value>
And so on
****
<First interaction associated with the third j-value>
<Second interaction associated with the third j-value>
<Third interaction associated with the first j-value>
And so on
Hamiltonian Ends

The first line has to state 'magnetic centres' and the second line will specify how many magnetic centres are there. Then the number of J-values are specified. After that the Hamiltonian is specified.

The spin interactions under a single J-value are specified in a single block. The spin interactions for different J-values are separated by '****'. The line 'Hamiltonian Ends' is needed in the end and is not preceded by '****'.

Note: The terms ‘magnetic centres’, ‘No. of J values’, ‘Hamiltonian’ and ‘Hamiltonian Ends’ are case-sensitive.

Examples of input files are provided in the Example Input Files subsection under the 'EJ_Calc' section and in the Example Input Files subsection under the 'Suscep' section.

File2 contains information about the the value of spin operators for each paramagnetic centre and the energy of different spin states. The format of this file is as follows:

 
<S11>  <S12>  <S13> ………. <E1>
<S21>  <S22>  <S23> ………. <E2>
<S31> <S32> <S33> ………. <E3>
…..
….

Here <S_ij> denotes the spin operator value for the j^th paramagnetic centre in the i^th electronic state and <E_i> represents the energy of the i^th state in Hartrees.

Examples of this input file are provided in the Example Input Files subsection under the 'EJ_Calc' section.

File3 contains the additional information other than the J-values required to calculate the temperature dependence of magnetic susceptibility and the format is as follows:

spin
<spin on the first paramagnetic centre>
<spin on the second paramagnetic centre>
<spin on the third paramagnetic centre>
And so on
g value
<g value>
Field Strength
<Field Strength (in Oersted)>
Temperature range
<Minimum temperature (in Kelvin)>
<Maximum temperature (in Kelvin)>
Step size
<Interval for temperature increments>

This is the format of File3. The first line has to state 'spin' and then the spin (number of unpaired electrons/2) on each paramagnetic centre is specified. This is followed by the definition of the g value which is then followed by the field strength (in Oersted) and temperature (in Kelvin). The final term is the step size for temperature (in Kelvin).

Note: The terms ‘magnetic centres’, ‘spin’, ‘No. of J values’, ‘g value’, ‘Hamiltonian’, ‘Field Strength’, 'Temperature range' and 'Step size' are case-sensitive.

Examples of this input file are provided in the Example Input Files subsection under the 'Suscep' section.

This file contains the magnitude of J-values to be used for the determination of magnetic susceptibility. The format of this file is shown below:

J values
<1st J-value (in cm-1)>
<2nd J-value (in cm-1)>
<3rd J-value (in cm-1)>
And so on

The first line contains the term ‘J values’ is followed by the strength of each J-value (in cm^-1) specified on separate lines.

Note: The term ‘J values’ is case-sensitive.

Examples of this input file are provided in the Example Input Files subsection under the 'Suscep' section.