I want to passivate the PbS crystal by an organic ligand like Formate. My atomic simulation does not converge and it's because I have not used proper molecular structure.
In the first 3 periods of the periodic table of elements, we use the octet rule. in the TM and Columns 3 to 12 we use the 18 electron rule. But I have no idea that what rule or method should I use for the Pb(Lead) + S(sulfur) + organic(formate) combinations.
thank you for your time
The simple answer is to recreate the same coordination environment (octahedral for PbS with an Fm-3m cubic crystal structure, the aristotype of which is the rock-salt structure) around each Pb atom as what Pb would have in the crystal. Cutting a crystal creates termini of the structure that take the form of planes, edges and corners. Complicating factors are the dependency of coordination by sulfur as a function of crystal face (in low-index faces of the crystal you may need only a whole number of formate anions, in higher-index faces, you may need fractions of a formate anion). For example, on a face one formate per Pb completes the octahedral coordination around Pb; this would correspond to a Pb atom imbedded on a planar site. On an cube edge, where two faces intersect at right angles, two formates would be needed; on a corner site, 3. On an edge where the angle of intersection is not 90 degrees, say between a face and a face, neither 1 nor 2 formates is really appropriate, so the electron-count is ideally between what would be donated by 1 and 2 formates. The sulfur ligands around Pb(II) on the surface donate electrons according to band theory. Approximately speaking, octahedrally coordinated Pb in the bulk of the crystal has 1/8 of each of 8 sulfur anions, contributing one lone pair each, totaling 2 electrons. A formate anion from solution in contact with the surface also donates 2 electrons, which is too much, because removing one sulfur from the surface Pb to create a 5-coordinate Pb gives the Pb not 2 electrons but 2-x, where x is approximately 1/6 of 2 electrons, or 2*1/6 = 1/3 = x. If x represents the "electron hole" at Pb on the surface, then formate should donate not 2 electrons but 1/3 of an electron. The left-over electrons, 2 - 1/3 = 5/3 = 1.666... electrons, then need to be shared (drained off) by something else (presumably by sharing with a cation from the solution, or shared with a proton or strong dipole from the solution, as in a hydrogen bond to water or solvent). A similar approximation applies to cubic corner and edge sites. You would need some way of splitting the number of formates (each donating 2 electrons) to get a number between 1 and 2 formates (for planar sites). Or you could restrict your investigation to only these three types of termini (planes, square edges and square corners), with idealized 6-coordination, and optimize the fractional occupancy of formate anions at those sites. At that point I am out of my depth, and you should study the software and ask questions from the software's technical support staff, concerning how best to model the formate coordination and calculate the number of electrons supplied by the formate anions. The issue of dynamics, in which the electron count fluctuates because diffusion of formates onto the crystals and off of the crystals gives at best some kind of average number of formates over a given period of time, also complicates these issues. Best wishes with your research. The study of interfaces between surfaces and fluids is not easy, so I'm sure anything your research can contribute to our understanding of the topic will be well-appreciated.
الإلكترون عبارة عن جزيء مشحون بشحنة سالبة يشكل جزءًا من الذرة، وتتكوّن كل العناصر الأساسية من الإلكترونات والبروتونات والنيوترونات. أحد المفاهيم الأساسية في علم الكيمياء هو القدرة على تحديد عدد الإلكترونات الموجودة في ذرة ما، ويمكن تنفيذ ذلك بسهولة باستخدام جدول العناصر الدوري. تتضمن مفاهيم الكيمياء المهمة أيضًا كيفية حساب عدد النيوترونات و إلكترونات التكافؤ (عدد الإلكترونات في أبعد غلاف خارجي للذرّة) لعنصر ما.
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