The　first　hyperpolarizabilities　of　four　squaric　acid　homologues:　squaric　acid,　1,2-dithiosquaric　acid,　1,2-diselenosquaric　acid　and　1,2-ditellurosquaric　acid　have　been　calculated　using　ab　initio　and　DFT　methods.　The　effects　of　equilibrium　geometries,　basis　set　and　electron　correlation　on　the　first　hyperpolarizabilties　of　these　molecules　were　investigated.　The　frequency　dispersion　effect　and　solvent　effect,　which　are　essential　to　get　reliable　outputs　in　comparison　to　the　experimental　results,　have　also　been　explored.　On　the　basis　of　these　investigations,　it　is　worthy　to　point　out　that　the　heavy　atom　effect　takes　effect　for　these　squaric　acid　homologues.