Pranayama or breathing techniques are a part of Yoga. They are good for general health, reducing the heart rate, BP and for calming the mind. They are excellent for depression, agitation, anger, anxiety and other mental issues.
Whether it will cure atheism is doubtful because Yoga itself is not necessarily theistic. It is secular and can even be considered atheistic in the sense that it focuses on Self development and not on finding God.
Self development however includes progressively moving towards a universal higher level of Consciousness. In that sense, pranayama can be considered as helping us in finding 'God'......since 'God' in Hinduism is a higher level of Consciousness that exists within us.