C60–C+60 collisions: Semiempirical molecular dynamics simulations

Abstract

Semiempirical molecular dynamics is used to study the collision of C60 and C+60. Particles are propagated classically using forces calculated from the modified neglect of differential overlap (MNDO) Hamiltonian. By assigning different collision energies (Ec) and impact parameters (b) to the Buckminster fullerenes (buckyballs), we simulated six collision events: four head on collisions with impact parameter b=0 and collisions energies of 100, 150, 200, and 400 eV, and two collisions with b=1.5 Rb (Rb=buckyball radius) and Ec=100 and 400 eV. The head on collisions show that at 100 eV the two buckyballs scatter off one another and at 200 and 400 eV they fuse, while at 150 eV they either scatter or form a metastable dimer depending on how the simulation is prepared. This barrier is consistent with recent experiments. In addition, we observe tetrahedral bonding in the C+120 structure formed in the 200 eV, b=0 collision, while at 400 eV, b=0 we see large rings and chains of carbon atoms. The off center collisions also display interesting structural features. In the 100 eV b=1.5 Rb collision, the buckyballs graze one another, distorting their cage structure and scattering at an angle relative to their incident velocities. The buckyballs in the 400 eV, b=1.5 Rb collision also scatter, but in contrast to the 100 eV, b=1.5 Rb collision, the individual buckyballs are severely distorted, forming what we refer to as an ‘‘open mouth’’ structure.

Non-adiabatic quantum molecular dynamics: basic formalism and case study

“…The last term in Eq. (18) has to be discussed in detail if the td single-particle functions ψ j are represented in a basis.…”

“…So far, most of the theoretical studies have been performed with the help of molecular dynamics (MD) calculations [16][17][18][19][20][21][22][23][24], in which the interatomic forces are calculated phenomenologically by two-or three-body interactions [16] or within tight-binding approximations [17][18][19]. Fully microscopic calculations -restricted to small systems -are based on classical MD combined with Hartree-Fock (HF) theory [20,21], density functional theory (DFT) [12,22] or approximate DFT [23, 24] -applicable also to larger systems -for the quantum electronic system.…”

Preferential synthesis and isolation of (6,5) single-wall nanotubes from one-dimensional C60 coalescence

“…Fullerene peapods have been demonstrated to be fused into double-wall carbon nanotubes (DWCNTs) by annealing at a temperature of 1200 C. 7,8 The dynamics of the coalescing process of fullerene molecules inside SWCNTs (10,10) has been investigated by topological analyses. 9,10 The C 60 fusion into different structures according to different collision energies was also investigated by tight-binding molecular dynamics 11 and semi-empirical molecular dynamics 12 methods. However, very limited experimental information on the structure of inner nanotubes has been reported.…”

Semiempirical MNDO, AM1, and PM3 direct dynamics trajectory studies of formaldehyde unimolecular dissociation

“…31,32,[42][43][44][45] The use of quantum mechanically derived energies and forces in molecular dynamics simulations is not new, 46,47 and, given increased computer performances, it has become more feasible. 28,[48][49][50][51][52][53][54][55][56][57][58][59][60][61] In addition to the extensive use of density-functional theory ͑DFT͒ methods in molecular dynamics simulations, such as the Car-Parrinello approach, 62 both ab initio and semiempirical molecular orbital ͑MO͒ theory methods are also being used in such simulations. Hartree-Fock ͑HF͒ ab initio molecular dynamics simulations 28,[47][48][49][50][51][52][53][54][55] are computationally so intensive that there is a need to develop integration algorithms which propagate the equations of motion with multiple scale stepsizes 53,54 or with very large stepsizes on local quadratic or higher order surfaces.…”

“…28,48,49 A less rigorous and computationally less expensive level of theory allows one to use standard simulation methods. A very practical approach lies in the use of semiempirical NDDO, 38 e.g., MNDO, 64,65 AM1, 66 and PM3, 67-69 molecular orbital methods, which have been successfully applied to small systems, 58 large systems 60,61 or only one part of a molecular system, with the remaining part described by empirical potential energy functions. 58,59 The evaluation of energy and gradients with a NDDO model is approximately 4 orders of magnitude faster than a HF ab initio calculation with a standard size basis set.…”