Alert account assigned user by email

Hi everyone!
I’m trying to set up workflow module to trigger some alerts and I’m having some trouble with it.
I have been reading some tutorials and some posts on the forum but still can figure my problem out.

Here’s what I would like to do:

  1. I have an assigned user on an account and another users security group on the same account (this is how I managed to have several users managing the same account)
  2. The user on the security group will eventually create an opportunity on that account
  3. I would like to alert the assigned user that there’s a new oportunity

The problem I have is that when the opportunity is created is assigned to the user creating it and not to the account “owner”. I can manage to send the email to the user that created the record but not the assigned user for that account.

I’m not sure if this is solvable or if I have to ask the users to create the opportunities under the “account owners” name…

Any ideias or tips?
In attach is my set up.