Adsorption Energy Calculation

Adsorption energy is defined as the decreasing energy when two materials are combined under the adsorption process in which an atom, ion, or molecule (adsorbate) is attached to the surface of a solid (adsorbent). Adsorption energy is obtained by calculating the difference between the energy of the adsorption model and the sum of the energy which separately calculated for each structure composing the adsorption structure. Adsorption energy, E_a, can be calculated as follows:

Therefore, in order to obtain the adsorption energy, scientists usually calculate the energies for the following three models: Slab supercell structure which is also called adsorbent, adsorption system which is the slab structure with the adsorbent, and adsorbate in the vacuum.

Application of Adsorption Energy Calculation

• Study the chemical engineering properties
• Explore the adsorption mechanism
• Determine the energetic heterogeneity of the surface of a solid

Figure 1. DFT calculations to investigate the catalytic performances of Niphosphide. (a) Optimized surface structures. (b) Free energy profiles. (Loco, D.; et al. 2015)

Our Adsorption Energy Calculation Workflow

At Alfa Chemistry, we have developed a mature workflow for calculating the adsorption energy of gas molecules on metal surfaces. Our reliable adsorption energy calculation process is as follows:

• Optimize the crystal structure of metals
• Establish and optimize the gas molecular structure model
• Build a metal surface structure model
• Relax the metal surface
• Optimize the metal surface and calculate the density of states of the system
• Add gas molecules structure on the metal surface and optimize the structure
• Energy analysis
• Density of states (DOS) analysis

Our Services

At Alfa Chemistry, we provide density functional theory, cluster model and molecular simulation methods to perform accurate adsorption energy calculation. Our fast and high-quality services include the following:

• Density functional theory (DFT)

We conduct large-scale DFT calculations to study the interaction between metal particle size and the covering effect of gas molecules.

1. We can study the adsorption of individual gas molecules at several adsorption sites on metal particles of different sizes.

2. Our experts also investigate in detail the influence of different ratios of gas molecule monolayer coverage, and calculate the adsorption energy of each gas atom of metal particles with multiple gas molecule coverage.

3. Moreover, according to the distribution of gas atoms of each metal particle size and the electron changes caused by adsorption on the metal particles, the dependence of the gas coverage of the adsorption energy of each gas atom is analyzed.

• Cluster model

Alfa Chemistry supports the calculation of solid surface reaction/adsorption based on quantum mechanics method. Our teams have established a cluster model to solve the surface calculation problems. We can perform calculation of the adsorption energy of gas/liquid molecules physically adsorbed on the metal surface. Our well-designed process is as follows:

(1) Construct the metal clusters

(2) Put the gas/liquid molecules into the metal cluster to get the initial structure of the composite

(3) Optimize the structure of the compound

(4) Calculate the single point energy of each segment

(5) Calculate the difference to obtain the adsorption energy

• Molecular simulation

The adsorption process is usually difficult to observe with experimental methods. Molecular simulation methods are useful tools to simulate the structure and behavior of molecules at the atomic and molecular levels, thereby revealing the mechanism of the adsorption phenomenon. At Alfa Chemistry, we use quantum mechanics method to simulate and study the adsorption of gas on the metal surface.

1. DFT in quantum mechanics combined with the periodic plate model is applied to calculate the vertical adsorption energy and adsorption structure of the gas on the metal surface.

2. The molecular dynamics (MD) method is used to simulate the diffusion of gas molecules on the metal surface, and the cluster analysis method is also applied to calculate the molecular diffusion coefficient.

• DFT combined with MD

We use DFT calculations combined with MD simulations to study the adsorption mechanism of gas on solid surfaces in aqueous media.

1. Our scientists use this technique to evaluate global reactivity descriptors such as frontier molecular orbital energy (EHOMO and ELUMO), interstitial energy (ΔE_gap), absolute hardness (η) and softening (σ), transferred electron fraction (ΔN) and electronegativity (χ).

2. The dynamic descriptors obtained by MD simulations are also calculated and discussed, such as adsorption energy (E_ads), total energy (E_tot), deformation energy (E_def), rigid adsorption energy (RAE) and dE_ads/d_Ni.

Alfa Chemistry's Advantages

• Our groups are capable of carrying out some wave function analysis on weak interactions.
• We improve the accuracy of the calculation results by testing the convergence of the calculated parameters:

1. Our experts use the significantly increased value of the vacuum layer thickness to repeat the calculation of chemical adsorption energy.

2. A more accurate k-point sampling density is applied to calculate the adsorption energy.

3. We can also enhance the reliability of adsorption energy calculation by adding the energy cutoff calculation.

• We help our clients to better understand the bonding mechanism between gas molecules and metal surfaces by studying the density of states.
• In addition to adsorption energy calculation, Alfa Chemistry provides additional services such as studying the best adsorption position of the molecule, the amount of molecules loaded on the surface, geometric configuration after adsorption and mechanism of adsorption.

Our adsorption energy calculation services remarkably reduce the cost, promote further experiments, and enhance the understanding of chemical process for customers worldwide. Our personalized and all-around services will satisfy your innovative study demands. If you are interested in our services, please don't hesitate to contact us. We are glad to cooperate with you and witness your success!

Reference

• Kim, J. Y.; et al. Predictive Fabrication of Ni Phosphide Embedded in Carbon Nanofibers as Active and Stable Electrocatalysts. Journal of Materials Chemistry A. 2019, 7: 7451-7458.