I am trying to compute UV/Vis absorption spectrum for Ethene using Gaussian 09.
I created the ethene molecule in GaussView 5, and cleaned it. Then I optimized the molecule and checked if I got the minimum energy conformation with the following:
# freq=noraman cphf=noread b3lyp/6-31g(d) geom=connectivity formcheck integral=grid=ultrafine scf=maxcycle=1000
Next I performed the energy calculation as follows:
# td b3lyp/6-31g(d) geom=connectivity
As a result I got a single peak with the maximum at 134 nm (see picture below) which seems to be way off from what I googled around on the Internet, which is like 173 nm or 180 nm.
Can anyone please help me figure out if I have done it correctly and whether I am way off the experimental data?