Viharas were for the purpose of living, Chaityas were assemblies for the purpose of discussions. Further, Chaityas were with Stupas, Viharas did not have stupas.
The last veda called the Atharva Veda is a collection of magic spells and charms to ward off the evil spirits and diseases. It is considered a non-Aryan work and is the latest addition to the Vedas in later Vedic age.
EXAMIANS