Research importance

THE PROPERTIES OF MACROSYSTEMS ARE THE OUTCOME of the microscopic interactions among atoms. Therefore, it becomes imperative to understand the microscopic state of matter to explain the stability, physical, chemical and thermodynamic features of different systems like crystals, alloys and ceramics. Our investigation has been focused in analyzing the processes of early formation and behavior of crystals with the use of atomic clusters. An atomic cluster is understood as a small bunch of atoms usually of the same nature. The bunch may be of nanometric size or slightly larger.

By growing atomic clusters (or increasing the number of atoms in the cluster) we can elucidate the evolution of important physical variables. We have investigated size-effects of atomic clusters of industrial and catalytic interest. Special attention has been given to clusters made of silver atoms as Mexico is one of the countries with major production. If we note that a macrocrystal only adopts a few conformations (phases), and the addition/substraction of a few atoms (of the same nature) or electrons hardly changes the crystal shape and reactivity, then we can identify atomic cluster not as simple small crystals, but as new entities with unique chemical properties because they present a reactivity that not only depends on the geometry, but also on the size and charge of the cluster. Due to these novel chemical aspects, atomic clusters have captured great attention in the last decade. The possible technological use of atomic clusters has lead to the creation of a new branch of science with the name "nanotechnology". The ultimate purpose of nanotechnology is to have control over the topology (geometry) and reactivity of atomic clusters for the creation of new materials and the implementation of more efficient processes.

Contribution to the research

QUANTUM PHYSICS HAS BEEN USED AS THE CENTRAL TOOL in combination with lower-level theories to establish the dependence of structural, electronic and thermodynamic quantities with the size of silver clusters. We designed a interaction potential that includes up to four-body terms. The potential was parameterized based on a great number of accurate DFT computations. In this regard, it was possible to quantify the role played by additive and non-additive forces in the formation of clusters, as well as the forces responsible for the 2-D to 3-D geometry unfolding. The interaction potential was capable to predict new stable structures that otherwise would be difficult to get through the use of the computationally costly ab-initio calculations.

Benefits for the Scientific Community and Society

THE 3-BODY PROBLEM IS WELL KNOWN IN PHYSICS. The presence of a third body when initially only two bodies were interacting greatly complicates the description of the system. In fact, it is not possible to achieve an accurate picture of the trimer by just working with interaction potentials by pairs. Therefore, our work on atomic clusters not only highlights the importance of three-, four- and many-body forces in the stability of clusters, but also shows the way to measure the deviation from the additive-force phenemenon, regardless we use ab-initio calculations or create a many-body interaction potential. Also, since researchers face strong problems to investigate, particularly from the experimental point of view, the electronic structure of small clusters, our work certainly complements measurements on size-effects achieved for larger atomic clusters still in the nanometric scale range. A clear understanding of the properties of small atomic clusters represents one important step towards the development of nanotechnology science.

Future projection

WE ARE MOTIVATED TO INVESTIGATE the electronic structure of matter under high pressure. For this, we are using tiny atomic clusters as crystal models inside molecular cavities that simulate environmental compression forces. Our objective is to determine the equation of state for each crystal we are dealing with. The study is expected to show the unsual behavior of matter under high pressures, which in nature may be achieved far downward in the earth. The importance of this investigation is also related to the better understanding of planet formation.