Density functional theory is used to show that the adhesion between single-walled carbon nanotubes (SWNTs) and the catalyst particles from which they grow needs to be strong to support nanotube growth. It is found that Fe, Co, and Ni, commonly used to catalyze SWNT growth, have larger adhesion strengths to SWNTs than Cu, Pd, and Au and are therefore likely to be more efficient for supporting growth. The calculations also show that to maintain an open end of the SWNT it is necessary that the SWNT adhesion strength to the metal particle is comparable to the cap formation energy of the SWNT end. This implies that the difference between continued and discontinued SWNT growth to a large extent depends on the carbon-metal binding strength, which we demonstrate by molecular dynamics (MD) simulations. The results highlight that first principles computations are vital for the understanding of the binding strength's role in the SWNT growth mechanism and are needed to get accurate force field parameters for MD.

IntroductionA primary goal of molecular modeling is the prediction of structure, stability, and chemical reactivity of molecules that are difficult to investigate by experimental means. Today, there are many methods ranging from simple structure descriptions to molecular mechanics and quantum chemical approaches to fulfill this goal. Each of these models is based on simplifications and assumptions, which should facilitate the task of molecular modeling. Molecular modeling does provide new insights into the properties of molecules and molecular reactivity provided one considers appropriately the assumptions and simplifications made within the model used.Despite the enormous potential and possibilities of molecular modeling with the help of advanced quantum chemiAbstract The bond energy (BE) of a polyatomic molecule cannot be measured and, therefore, determination of BEs can only be done within a model using a set of assumptions. The bond strength is reflected by the intrinsic BE (IBE), which is related to the intrinsic atomization energy (IAE) and which represents the energy of dissociation under the provision that the degree of hybridization is maintained for all atoms of the molecule. IBE and BE differ in the case of CC and CH bonds by the promotion, the hybridization, and the charge reorganization energy of carbon. Since the latter terms differ from molecule to molecule, IBE and BE are not necessarily parallel and the use of BEs from thermochemical models can be misleading. The stretching force constant is a dynamical quantity and, therefore, it is related to the bond dissociation energy (BDE). Calculation and interpretation of stretching force constants for local internal coordinate modes are discussed and it is demonstrated that the best relationship between BDEs and stretching force constants is obtained within the model of adiabatic internal modes. The valence stretching force constants are less suitable since they are related to an artificial bond dissociation process with geometrical relaxation effects suppressed, which leads to an intrinsic BDE (IBDE). In the case of AX n molecules, symmetric coordinates can be used to get an appropriate stretching force constant that is related to the BE. However, in general stretching force constants determined for symmetry coordinates do not reflect the strength of a particular bond since the related dissociation processes are strongly influenced by the stability of the products formed.Keywords Bond energy (BE), Intrinsic bond energy (IBE), Bond dissociation energy (BDE), Force constants, Adiabatic internal mode cal methods, there is still a need to understand the properties and behavior of molecules on the basis of simple models that require no sophisticated calculations. One wants to connect the properties of a molecule with those of atoms, bonds, or small functional groups so that the knowledge of these group properties makes it possible to describe whatever molecule may be constructed from atoms, bonds (diatomic groups) or functional groups. Central to many of the...

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