Ab initio molecular dynamics
A key feature of Qcore is the capability to perform efficient classical and quantized path-integral molecular dynamics (MD) simulations using on-the-fly electronic structure potential energy surfaces, including GFN-xTB, DFT and EMFT.
The minimal input for running an ab initio molecular dynamics simulation looks like this:
aimd( structure(molecule = water) n_steps = 1000 time_step = 0.5 fs xtb() )
This input corresponds to an MD trajectory simulation of water starting from a built-in geometry, with an integration step size of 0.5 fs and a total number of 1,000 integration steps (which gives a total simulation time of 0.5 ps). The energy and forces are evaluated at GFN-xTB level of theory. The initial velocities are set to zero by default, and no thermostat is applied.
Additional simulation options/subcommands can be found in the user manual. Here, we show another example to illustrate options/subcommands for running a thermalization trajectory using the Andersen thermostat:
aimd( structure(molecule = water) n_steps = 1000 time_step = 0.5 fs gradient( xtb() ) velocities( sampling = thermal temperature = 300 kelvin ) thermostat( type = andersen temperature = 300 kelvin ) )
Here, we generate the initial velocities from Maxwell-Boltzmann distribution at 300 K, by specifying
sampling = thermal in the
velocities() subcommand. We apply the Andersen thermostat to the trajectory with target temperature of 300 Kelvin.