Ab initio molecular dynamics: Propagating the density matrix with Gaussian orbitals. III. Comparison with Born–Oppenheimer dynamics

Abstract

In a recently developed approach to ab initio molecular dynamics ͑ADMP͒, we used an extended Lagrangian to propagate the density matrix in a basis of atom centered Gaussian functions. Results of trajectory calculations obtained by this method are compared with the Born-Oppenheimer approach ͑BO͒, in which the density is converged at each step rather than propagated. For NaCl, the vibrational frequency with ADMP is found to be independent of the fictitious electronic mass and to be equal to the BO trajectory result. For the photodissociation of formaldehyde, H 2 CO→H 2 ϩCO, and the three body dissociation of glyoxal, C 2 H 2 O2→H 2 ϩ2CO, very good agreement is found between the Born-Oppenheimer trajectories and the extended Lagrangian approach in terms of the rotational and vibrational energy distributions of the products. A 1.2 ps simulation of the dynamics of chloride ion in a cluster of 25 water molecules was used as a third test case. The Fourier transform of the velocity-velocity autocorrelation function showed the expected features in the vibrational spectrum corresponding to strong hydrogen bonding in the cluster. A redshift of approximately 200 cm Ϫ1 was observed in the hydroxyl stretch due to the presence of the chloride ion. Energy conservation and adiabaticity were maintained very well in all of the test cases.

Experimental and Ab Initio Dynamical Investigations of the Kinetics and Intramolecular Energy Transfer Mechanisms for the OH + 1,3-Butadiene Reaction between 263 and 423 K at Low Pressure

“…This approximation has been found to provide reasonable approximations to cluster temperature for a variety of ADMP studies. 52,54,55,[60][61][62][63][64][65] The vibrational-energy-transfer mechanism was probed by considering (a) the evolution of the Fourier transform of the velocity-velocity autocorrelation function (FT-VAC) as a function of time for the full molecule as well as the individual fragments, (b) a detailed analysis of the evolution of contributions from the individual Harmonic modes (to be discussed in section VI(c)) as a function of time, and (c) the evolution of the individual fragment kinetic energies as a function of time. It must be noted that the FT-VAC provides a representation of the vibrational density of states sampled during finite temperature simulations.…”

Ab Initio Molecular Dynamics with Born-Oppenheimer and Extended Lagrangian Methods Using Atom Centered Basis Functions

“…[71][72][73] These features, coupled with the extensive experience that the chemistry community has with levels of theory and basis sets, lead us to develop the atom-centered density matrix propagation (ADMP) method for molecular dynamics. [74][75][76] The equations for propagation of the density matrix are simplest in an orthonormal basis. In many ways, this is similar to density matrix search methods for calculating electronic energies.…”

“…The ADMP approach wins for larger systems and shows its advantage even earlier for hybrid DFT methods. 76 The ADMP method has some of the specific advantages and greater flexibility when compared to the Car-Parrinello approach. All electrons can be treated explicitly and pseudopotentials are not required.…”

“…Smaller fictitious masses can be used and good adiabaticity can be maintained without thermostats. [74][75][76] For ionic systems, vibrational frequencies calculated by the plane-wave Car-Parrinello method show a disturbing dependence on the fictitious electronic mass; 84 however, the ADMP method is free from this problem. 76 The ADMP trajectories compare very well with those computed by BO methods.…”

“…[74][75][76] For ionic systems, vibrational frequencies calculated by the plane-wave Car-Parrinello method show a disturbing dependence on the fictitious electronic mass; 84 however, the ADMP method is free from this problem. 76 The ADMP trajectories compare very well with those computed by BO methods. 74 Specifically, for CH 2 O → H 2 + CO and C 2 H 2 O 2 → H 2 + 2 CO, the ADMP trajectories give product translational, rotational and vibrational energy distributions that are very close to the BO results.…”