Benchmark full-CI calculation on C2H2: comparison with (SC)2-CI and other truncated-CI approaches

Large-scale full configuration interaction (FCI) calculations are presented on the acetylene molecule using several basis sets. The largest calculation involves more than five billion symmetry-adapted Slater determinants. The FCI results are compared with those obtained using the (SC)2-CI method, that corrects the size-consistency defect of truncated CI schemes. A comparison with other truncated-CI calculations, of both contracted and uncontracted type, is also done.