is it possible to apply voltage in molecule level

[Val]

sir,
     from the Script generator new calculator charge option was not available in 10.8 but in 11.2 charge option is available.could you explain the use of that charge option.

    i need to apply voltage to GNR without source and drain.By varying the applied voltage i need to find out the Eg of GNR(in molecule level not in device level).could you explain me the procedure for how to do it.

[Anders Blom]

The charge option was available in ATK 10.8 too, but not in the Scripter (you had to edit the script manually to set it). The parameter can be used for molecules and bulk systems to add or remove charge. By setting the charge to -1 you remove one electron from the system. A detailed explanation on how to use this to calculate accurately the electron affinity of molecules is given in the benzene SET tutorial.

Note that the parameter can only be used in systems with a fixed number of electrons. To change the charge in a transport system, it is necessary to shift the Fermi level. This can be done by introducing a gate (like in the graphene device tutotial). Perhaps this is similar to what you are interested in achieving?