LiO

Quantum Calculations for Lithium Monoxide

This page contains

the optimized geometry
the highest occupied molecular orbital
potential energy of bond stretching
vibrational frequency data
dipole moments and partial charges

LiO Optimized Geometry

The most optimal geometry was determined by the conformation with the lowest energy. MOPAC was used to guess an initial geometry, which was then given to MacMolPt to set up calculations. The calculations were run in GAMESS at three different levels of theory. After each theory calculation, the lowest energy conformation was used as the beginning guess for the next level. When the calculation finally converged at the DZV level, that conformation had the lowest energy and was determined to be the best geometry.

The most optimal geometry for LiO turned out to have a bond length of 1.74 Angstroms between the atoms.

Lit comparison: The literature³ gave an experimental value of 1.688 Angstroms between the atoms. So the calculations were a little off, which is to be expected because the calculations are based on approximations, not exact values.

LiO HOMO

The highest energy molecular orbital that is occupied by electrons is called the HOMO. The HOMO of LiO is shown to the right. This particular orbital is nonbonding, because it does not extend to include both atoms.

Potential Energy of Bond Stretching

The graph below shows the potential energy for all three levels of theory. The DZV level (the blue line) has the lowest potential energy, and thus is the best approximation for opitmized geometry. This is yet another indication that bigger basis sizes are needed for best results.
Potential Energy of Bond Stretch Graph

Vibrational Frequency

The vibrational frequency data calculated only included one vibrational peak, at 816.23cm^-1.

Getting a Better Dipole
Dipole moments were obtained from a previous experiment, but then were recalculated with diffuse functions in order to get a better dipole. The calculation was run three times, each with a different number of polarization functions for D heavy atoms and light atoms (represented by 111, 212, and 313). The number for F heavy atoms, which is the central number, was required to be always 1. The electrostatic moments and partial charges are shown below for each calculation.

Electrostatic Moments: X, Y, Z in bohr; DX, DY, DZ in debye.

	X	Y	Z	Charge(AU)	DX	DY	DZ	/D/
111	0	0	.066962	.00	0	0	-6.923281	6.923281
212	0	0	.066962	.00	0	0	-6.905664	6.905664
313	0	0	.066962	.00	0	0	-6.992058	6.992058

Partial Charges
111

Atom	Mull. Pop.	Charge	Low. Pop.	Charge
Li	2.335124	.664876	2.778553	.221447
O	8.664876	-.664876	8.221447	-.221447

212

Atom	Mull. Pop.	Charge	Low. Pop.	Charge
Li	2.370560	.629440	2.814017	.185983
O	8.629440	-.629440	8.185983	-.185983

313

Atom	Mull. Pop.	Charge	Low. Pop.	Charge
Li	2.399572	.600428	2.810366	.189634
O	8.600428	-.600428	8.189634	-.189634

The results here are not necessarily better with bigger basis sets. It turns out that the number of functions does not matter so much with dipole moments -- better results are obtained through the addition of a few large and specific polarization functions.

Literature Comparison: The literature³ gave an experimental value of 6.843 in the Debye. The calculated dipole moment is greater than this, but only by about 1%.

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Based on template by A. Herráez as modified by J. Gutow

Page skeleton and JavaScript generated by export to web function using Jmol 11.8.20 2010-02-28 19:28 on Mar 17, 2010.

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