Intertek ASG Laboratory, Manchester, UK > Computational Chemistry Group > Electronic Property Prediction

Electronic Property Prediction

The properties of neutral or charged molecules in their ground or excited states can be probed. The electronic structure of a molecule, expressed by properties such as the charges on the individual atoms or the nature of the molecular orbitals can be calculated. Values for the Ionisation Potential (IP) and Electron Affinity (EA) can be generated for comparison with electrochemical data. For excited states, the enery and nature of all of the electronic transitions of the molecule can be calculated and visualised to gain an understanding of the nature and effects of the electronic excitation.

To find out more on each of these areas, see below:

• Atomic Charges
• Molecular Orbitals
• Ionisation Potential and Electron Affinity
• Electronic Transitions

Atomic Charges

Using a variety of methods, charges can be calculated for each atom within a molecule. These charges can be used to help understand properties such as:

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Molecular Orbitals

Molecular Orbitals (MOs) can be used to visualise the location of electrons within a molecule. The shapes and locations of the orbitals can be used to provide information about bonding within the molecule. Often, the HOMO (Highest Occupied MO) and LUMO (Lowest Unoccupied MO) are used to help understand reactivity, and the energy difference between these two orbitals is often used as an approximation of the ease with which the molecule might be excited.

Ionisation Potential and Electron Affinity

Electrochemical measurements can be used to generate the oxidation potentials of a molecule - the ease with which electrons can be removed. Computationally, the same properties can be predicted in the form of Ionisation Potentials (IP). These are of particular use when studying electronic materials. The opposite of the Ionisation Potential is the Electron Affinity (EA) - the ease with which an electron can be added. These two properties can be used to gain an understanding on the stability or reactivity of a molecule.

An extension to IP and EA are Fukui functions. These can be used to give a 3D spatial indication of which parts of the molecule are susceptible to attack by:

Electronic Transitions

Understanding the nature of an excited state can be important when dealing with:

Experimental methods such as UV/vis spectroscopy and various electrochemical techniques can provide some information on processes such as absorption of light or oxidation but to start to characterise the excited state more fully is usually very hard and often expensive. Using a combination of state of the art ab initio packages and other software developed in-house, individual excited states can be probed and the nature of the transition between the ground state and an excited state of interest can be described.

This approach can be used to predict the energy of the transition and its associated oscillator strength (related to intensity). The effects of the transition on the electronic properties of the molecule can be investigated by visualising properties such as the electron density difference between two states. Spectra can be simulated from the calculated data for comparison with experimental results.