Multiwfn forum

sobereva

Tian Lu (Multiwfn developer)

From: Beijing

Registered: 2017-09-11

Posts: 1,830

Website

Evaluate amount of charge transfer and direction

A Multiwfn user recently asked me how to study charge transfer between adsorbate and adsorbent, the charge transfer and direction information are needed to be obtained. Below is my reply, which may be useful for other users.

If the charge transfer you mentioned does not come from electron excitation process but purely result from intermolecular interaction, you can study amount of charge transfer based on variation of fragment charge, which is defined as the sum of charges of the atoms in the fragment. Evidently, the fragment could be defined as adsorbate or adsorbent. The fragment charge could be directly outputted by Multiwfn, namely entering main function 7, using option -1 to define a fragment, and selecting one of methods to carry out atomic charge evaluation (the ADCH proposed by me is generally recommended), you will find fragment charge at the end of the output.

An alternative method is plotting density difference map between complex and all fragments, see Section 4.5.5 for example, the charge displacement can be vividly revealed. In addition, if you want to quantitatively represent charges transfer distance and direction during the adsorption, you can first calculate grid data of density difference, and then use subfunction 3 of main function 18 to transform/quantify the density difference (see the example in Section 4.18.3 of the latest version of manual. Although this method was originally proposed for studying charge transfer during electron excitation process, it can also be applied for other cases)

Finally, in certain case, plotting charge displacement curve is useful, see the example in Section 4.13.6.