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HOMO-LUMO Calculation and Analysis Using DFT method in Gaussian Software

 




HOMO and LUMO are terms used in chemistry to refer to the Highest Occupied Molecular Orbital (HOMO) and the Lowest Unoccupied Molecular Orbital (LUMO), respectively. These orbitals are important in understanding the electronic structure and reactivity of molecules, especially in the context of organic and inorganic chemistry and chemical reactions.

 

HOMO (Highest Occupied Molecular Orbital):

 

The HOMO represents the highest energy level of molecular orbitals that contain electrons. It is typically involved in chemical bonding and determines the electron-donating properties of a molecule.

In terms of significance:

It dictates the reactivity of a molecule in nucleophilic reactions. Molecules with higher energy HOMOs are more prone to donate electrons and act as nucleophiles.

It plays a crucial role in determining the absorption spectrum of molecules. Absorption of light often involves promotion of electrons from the HOMO to the LUMO or higher energy orbitals, depending on the energy of the incident light.

In organic chemistry, it's relevant in understanding the stability and reactivity of reactive intermediates like carbocations, carbanions, and radicals.

LUMO (Lowest Unoccupied Molecular Orbital):

 

The LUMO represents the lowest energy level of molecular orbitals that is unoccupied by electrons. It is primarily involved in accepting electrons and determines the electron-accepting properties of a molecule.

In terms of significance:

It dictates the reactivity of a molecule in electrophilic reactions. Molecules with lower energy LUMOs are more prone to accept electrons and act as electrophiles.

Understanding the mechanisms of various chemical reactions is crucial, especially regarding the interaction between electron-rich and electron-poor species.

In the context of materials science and semiconductor physics, the energy difference between HOMO and LUMO determines the conductivity and optical properties of materials. For example, in organic semiconductors, the HOMO-LUMO gap (energy difference between the two) affects the material's ability to conduct electricity and absorb light.

In summary, HOMO and LUMO frontier orbitals are significant because they provide insights into the reactivity, stability, and optical properties of molecules, which are fundamental to understanding various chemical processes and designing new materials with specific properties.

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