Emailing HOD to enhance faculty application

To stand out from the rest of the applicants and to bring to attention the application to the head of the department (HOD), would emailing the HOD enhance my application or would it affect it negatively.

Realistically, it does not affect your application at all. Firstly, this does not make you "stand out" nearly as much as you think it does, because quite a few people have the idea that writing some sort of personal letter to the head of the hiring committee improves their chances. Secondly, what do you expect will realistically happen? That the HoD thinks "gee, nxkryptor certainly shows initiative, better put them on the shortlist"? This is really not how academic hiring works.

The most realistic effect is that the HoD sees your email among the >100 mails of the day, exhales a short sigh, and then either directly moves it to "read" or writes you a polite "thanks for letting me know". 120 seconds later they have forgotten your name again, and it won't impact the evaluation of your package in any noticeable way.

First, the person most involved with a search is the chair of the search committee. Sometimes this is the HoD, but often it is not. Sometimes the HoD is on the search committee and sometimes they are not. Often, and in my opinion ideally, the HoD is not involved in the search until the end.

Now to answer your question. If you know someone in the department you can, and should, email/call them that you are applying. You should also ask for whatever inside information they have. If you have questions (e.g., I am in subfield X, is that within the scope of the search), then you can email search chair (or whoever the contact point is).

Do not email the head of department, the chair of the search or anyone on the search committee in an attempt to stand out from the rest of the applicants. That is surely going to backfire.