Recently, we performed the time-dependent (TD) density functional theory (DFT) calculations on the tetraphenylehtene – bis(thiophen-2-methyl)amine (TPE-BTA), which shows a turn-on bright green fluorescence along with high sensitivity toward Hg2+, to discover the structures of TPE-BTA complex with Hg2+. However, we found that only x2c-TZVPPall, all electron (AE) basis set, for the Hg2+ ion successfully reproduces the absorption and vibrationally resolved fluorescence spectra close to the experimental spectra [1], but the tested effective core potential (ECP) basis set, LANL2DZ, failed to optimize the excited state geometries related to the fluorescence spectra calculations. In addition, LANL2DZ provided too small fluorescence energies during optimization process of the first excited state. LANL2DZ provides the rapidly decreased HOMO-LUMO gaps with the distance between ligand and Hg2+ increased whereas x2c-TZVPPall calculates gradually decreasing HOMO-LUMO gaps. We cautiously suggest that at least the system containing Hg2+ ion should be calculated using all electron basis set to escape from geometrical erroneous behavior coming from ECP basis sets.