Talk to Psychologist on PostRetirement Depression

AOA, My father is suffering from post-retirement depression. He has been dealing with it since two years now. It gets better or worse in phases. Nowadays it's at the worst from ever. He sometimes has suicidal thoughts. He always thinks about all the negative possibilities of any life situation. He is generally very apologetic for being depressed and putting his family through it. He is been losing temper more often lately and now it's really starting to worry me (like any daughter). Can you please suggest any solution or refer me to the best psychiatrist for my father ? Thank you. Regards.