Comparing B3LYP and B97 dispersion-corrected functionals for studying adsorption and vibrational spectra in nitrogen reduction

Abstract

Electrochemical ammonia synthesis is being actively studied as a low temperature, low pressure alternative to the Haber-Bosch process. This work studied iridium as the electrochemical catalyst, following a previous study of adsorption characteristics on platinum. The characteristics studied include bond energies, bond lengths, spin densities, and free and adsorbed vibrational frequencies for the molecules N2, N, NH, NH2, and NH3. Overall, these descriptive characteristics explore the use of dispersioncorrected Density Functional Theory methods that can model N2 adsorption-the key reactant for electrochemical ammonia synthesis via transition metal catalysis. Specifically, three methods were tested: hybrid B3LYP, a dispersion-corrected form B3LYP-D3, and semi-empirical B97-D3. The latter semi-empirical method was explored to increase the accuracy obtained in vibrational analysis as well as reduce computational time. Two lattice surfaces, (111) and (100), were compared. The adsorption energies are stronger on (100) and follow the trend EB3LYP > EB3LYP-D3 > EB97-D3 on both surfaces.

Density functional theory study of Mobius boron-carbon-nitride as potential CH 4 , H 2 S, NH 3 , COCl 2 and CH 3 OH gas sensor

“…where E (MBCN + gas, ZPE) , E (MBCN, ZPE) and E (gas, ZPE) are the zero-point corrected energy of the MBCN + gas complex structure, pristine MBCN and gas molecules, respectively [23]. The B3LYP method cannot describe the dispersion among molecules to provide higher accuracy of adsorption [24]; hence we incorporated the dispersion-corrected B3LYP-D3 calculation to obtain the dispersion-corrected adsorption energy (E Ads, Disp ) from the following equation: E Ads, Disp ¼ E (MBCNþgas, Disp) À E (MBCN, Disp) À E (gas,Disp) , ð2:4Þ…”

“…where E (MBCN + gas, Disp) , E (MBCN, Disp) and E (gas, Disp) are the dispersion-corrected energy of the MBCN + gas complex structure, pristine MBCN and gas molecules, respectively [19,24,25].…”

“…The B3LYP method cannot describe the dispersion among molecules to provide higher accuracy of adsorption [24]; hence we incorporated the dispersion-corrected B3LYP-D3 calculation to obtain the dispersion-corrected adsorption energy ( E Ads, Disp ) from the following equation:EAds, Disp=Efalse(normalMBCN+normalgas,normalDispfalse)−Efalse(normalMBCN,normalDispfalse)−Efalse(normalgas,normalDispfalse),where E (MBCN + gas, Disp) , E (MBCN, Disp) and E (gas, Disp) are the dispersion-corrected energy of the MBCN + gas complex structure, pristine MBCN and gas molecules, respectively [19,24,25].…”