XAlkeneDB: A database illuminating the electronic ground and excited state quantum chemical features of ethene, propene and butene

XAlkeneDB: 01_3Sing_C2H4.db, 02_3Sing_C3H6.db, and 03_3Sing_C4H8.db

The data of 01_3Sing_C2H4.db, 02_3Sing_C3H6.db, and 03_3Sing_C4H8.db, i.e. the XAlkeneDB was generated in three main steps:

1. Generating alkenes with HC=CH dihedral angles from 0 to 180°
2. Sampling of displaced geometries along this path, and
3. Computation of electronic properties.

Equilibrium geometries for ethene (C2H4), propene (C3H6), and butene (C4H8) were determined using DFT at PBE0/def2TZVP level of theory, covering both cis- and trans-isomers for butene. Vibrational analysis ensured these geometries corresponded to energy minima.

To broaden the configurational space, structures with various HC=CH dihedral angles were sampled, including 11 intermediate structures for butene connecting the cis- and trans-isomer, and 5 structures beyond equilibrium for ethene and propene. Subsequently, Wigner sampling augmented the initial 6 (ethene/propene) or 13 (butene) geometries connected on the alkene bond rotation path by 1000 structures each, facilitating sampling of vibrational degrees of freedom.

Ground- and excited-state properties were computed for all 25,000 generated structures (6,000 for ethene/propene and 13,000 for butene) using SA(3)-CASSCF(2,2)/cc-pVDZ level of theory. The dataset encompasses potential energies ('energy'), atomic forces ('forces'), permanent and transition dipole moments ('dipoles'), and non-adiabatic coupling vectors ('nacs') for each structure.

 

The databases 04_3Sing_C2H4_grid.db, 05_3Sing_C3H6_grid.db, and 06_3Sing_C4H8_grid.db contain quantum chemical reference data collected on a 2D-potential energy surface consisting of 3731 points (41x91 points). This grid was generated based on the most stable equilibrium geometry of ethene, propene, and butene, respectively. We scanned the alkene C=C bond distance between 2.000 and 3.000 Bohr in steps of 0.025 Bohr (41 steps) and varied the HC=CH dihedral angle from 0 to 180° in 2° increments (91 steps). Electronic properties for each geometry were obtained at the SA(3)-CASSCF(2,2)/cc-pVDZ level of theory for the three lowest-lying singlet states.