Based on the small amount of information it is possible this is abandonment, but like was said above there's fine print in the contract and state laws. We really can't answer.
This doesn't answer the question, but if you're quitting knowing the organization can't accommodate patients AND-there's nothing significant that makes you want to leave (e.g. an emergency, you have to get out of the area for whatever reason, the employer is being inappropriate on some level where your continued work there enables it, etc), whether or not this is illegal it is unethical by a Hippocratic Oath standpoint because you have a doctor-patient relationship with these patients. Whether or not that matters to you is up to you, but we're not in a profession where we are supposed to act as mercenaries. This is why Abandonment is an issue in medicine and why several states and specific laws on what constitutes abandonment, because in our profession we can't just get up and leave at a moment's notice. We're not burger flippers. We're doctors.
Now if the employer is being unfair or you have significant reasons why you want out that are exceptional that's different(e.g. you need to move cause you found out your father living on the other side of the country had early stage dementia, or you found out the employer is doing something illegal), but if it's cause of something like you just don't feel like it, it may be legal, it may not be-again that's where the legal fine print answers, but this is not ethical and if it were that type of situation-I would not want to work with you in my own practice. If I ever found out a colleague abandoned patients there's no way in hell I'd want to work with this person. Also it's not like there's a million psychiatrists in a locality. You flake out people in the area will likely find out as many doctors and other providers in a town know each other.
If the organization can't accommodate patients and you want out, then you should terminate your doctor patient relationship and then get the hell out of there by offering prescriptions to give patients time to find a new doctor and referrals. Some areas you need to give a legally defined warning such as 1 month or even more. Many institutions demand 3 months. I used to live in Ohio-it required a newspaper add, or a sign on the office waiting room. Many states have laws that even after you're gone for up to a certain amount of years you are responsible to still provide medical records upon request.