Ethically it's not how things should be done in the business world. This won't be the last time you come across an employee or client you won't get a long with. It happens and it can be toxic for the work environment and other employees.

A couple months severance pay is a nice gesture. I would explain to the employee you think they are great and highly talented, but you feel as though they are not the right fit for team and environment. Acknowledge conflicts, but whatever you do, don't go pointing fingers and shifting blame.

Amicably end the employment and offering a couple months severance pay will ensure that it definitely ends amicably. Most people don't find themselves in a situation where an employer is willing to compensate for things the employee cannot change.