Ok to break lease?

Tomorrow, my husband and i are starting the process of closing on a home. However, we are tied to a lease now until August. We are supposed to close within 30 days so that will leave us with a couple of months left on the lease. Is there some kind of unwritten rule or understanding that if you are buying a home, you can break the lease and the landlord will not penalize you? Is there some type of letter i can compose to state our intent to move because we are buying??