Monte Carlo simulations of temperature-programmed desorption spectra

We show how to obtain good quantitative data on the energetics of surface reactions by fitting results of dynamic Monte Carlo simulations to results of kinetic experiments. In particular, we can obtain numerical values for various lateral interactions by simulating temperature-programmed desorption spectra and fitting the simulated spectra to the experimental ones using evolution strategies. We illustrate the procedure by determining nearest-, next-nearest-, and next-next-nearest-neighbor interactions for CO on Rh(100). ©2004 The American Physical Societ

Kinetic Monte Carlo method for simulating reactions in solutions

We present an off-lattice kinetic Monte Carlo method, which is useful to simulate reactions in solutions. We derive the method from first-principles. We assume that diffusion leads to a Gaussian distribution for the position of the particles. This allows us to deal with the diffusion analytically, and we only need to simulate the reactive processes. The rate constants of these reactions can be computed before a simulation is started, and need not be computed on-the-fly as in other off-lattice kinetic Monte Carlo methods. We show how solvent molecules can be removed from the simulations, which minimizes the number of particles that have to be simulated explicitly. We present the relation with the customary macroscopic rate equations, and compare the results of these equations and our method on a variation of the Lotka model

Bayesian approach to the calculation of lateral interactions: NO/Rh(111)

We show how Bayesian statistics and density-functional theory can be combined to compute reliable values for the interactions in a cluster expansion for adsorbates on a surface. The method is an alternative to the leave-one-out cross-validation method. We show that it easily selects which interactions can be determined even if the total number of possible interactions is very large. We have applied the method to NO/Rh(111). Based on the interactions we have determined for this system we have predicted some structures, which have been confirmed by scanning-tunneling microscopy

Potential energy surfaces for Rh-CO from DFT calculations

We present potential energy surfaces for Rh-CO obtained from d. functional theory for two electronic states of Rh-CO. We have performed local spin-d. calcns. including relativistic as well as gradient corrections. The construction of a reasonably accurate atom-atom potential for Rh-CO is not possible. We were much more successful in constructing the potential energy surfaces by representing the potential as a spherical expansion. The expansion coeffs., which are functions of the distance between the rhodium atom and the carbon monoxide center of mass, can be represented by Lennard-Jones, Buckingham, or Morse functions, with an error of the fit within 10 kJ/mol. The potential energy surfaces, using Morse functions, predict that the electronic ground state of Rh-CO is 2S+ or 2D. This is a linear structure with an equil. distance of rhodium to the CO center of mass of 0.253 nm. The bonding energy is -184 kJ/mol. Morse functions predict that the first excited state is 3A'. This is a bent structure (?Rh-CO - 14 Deg) with an equil. distance of rhodium to the carbon monoxide center of mass of 0.298 nm. The bonding energy of this state is -60 kJ/mol. Both these predictions are in good agreement with the actual d. functional calcns. We found 0.250 nm with -205 kJ/mol for 2S+ and 0.253 nm with -199 kJ/mol for 2D. For 4A', we found 0.271 nm, ?Rh-CO = 30 Deg, with -63 kJ/mol. The larger deviation for 4A' than for 2S+ or 2D is a consequence of the fact that the min. for 4A' is a very shallow well. [on SciFinder (R)

Perspective on "Self-consistent molecular Hartree-Flock-Slater calculations", Baerends,EJ, Ellis,de, Ros,P (1973) Chem Phys 2:41

This paper discusses the title paper by Baerends, Ellis, and Ros. We show the role it has played in the development of density functional theory and the further work it has initiated

A Monte Carlo study of temperature-programmed desorption spectra with attractive lateral interactions

We present results of a Monte Carlo study of temperature-programmed desorption in a model system with attractive lateral interactions. It is shown that even for weak interactions there are large shifts of the peak maximum temperatures with initial coverage. The system has a transition temperature below which the desorption has a negative order. An analytical expression for this temperature is derived. The relation between the model and real systems is discussed.Comment: Accepted for publication in Phys.Rev.B15, 10 pages (REVTeX), 2 figures (PostScript); discussion about Xe/Pt(111) adde

Formation of ordered structures of NO on Rh(111)

In this work, several (unreported) structures of NO on Rh(111) are presented for coverages ranging from 0-0.78 ML. The formation of these structures as evidenced experimentally by scanning tunneling microscopy (STM) images is explained using density-functional theory derived values for the lateral interactions and adsorption energies of NO on Rh(111). Kinetic Monte Carlo simulations using the derived lateral interactions are performed to determine structures at finite temperatures. The resulting structures can be directly compared to the molecular arrangements observed in the STM experiment. The configuration of the first three structures that form for increasing coverage is the same both experimentally and theoretically. In all three structures, the molecules only occupy the fcc and hcp adsorption sites. Yet, at high coverage, at which the top adsorption sites become occupied, a discrepancy arises

Vibrations of adsorbates on metal surfaces from geometry optimizations

We present a method to compute harmonic vibrations that uses the structures and the forces in the structures that are obtained from a geometry optimization. It does not require any additional electronic structure calculations. The method generally takes only on the order of minutes on a regular PC, but it does not guarantee the calculation of all vibrations of a system. Tests on small adsorbates on a transition metal surface show, however, that the most relevant vibrations are obtained. An important part of the method is the inclusion of several checks to determine the reliability of its results, which gives also error estimates of the vibrational frequencies

An Ab Initio embedded cluster study of the adsorption of NH3 and NH4+ in chabazite

The adsorption of NH3 in acidic zeolites has been studied extensively experimentally. Therefore, it can be used very well to verify a model used in a quantum chemical calculation. Here, we present a calculation that, from a quantum chemical point of view, should give a reliable description of the adsorption process. We studied the adsorption of NH3 and NH4+ in chabazite with the embedded cluster method using a reasonable basis set, applying the counterpoise correction and including electron correlation. The geometry was partially optimized. With this calculation we verified the reliability of our model and obtained information that cannot be obtained experimentally. The adsorption energies of hydrogen-bonding NH3 and of NH4+ were -70 +/- 10 kJ/mol and -120 +/- 15 kJ/mol, respectively. The latter value compares very well with the experimental heat of adsorption. NH4+ has a high coordination with the zeolite wall; this is confirmed experimentally. A good geometry is obtained if the boundary of the embedded cluster is kept fixed to that of the zeolite crysta