One of the distinguishing aspects of CP2K is its seamless integration of diverse structural and transition-state optimization techniques with advanced sampling approaches including Monte Carlo, molecular dynamics, and metadynamics, enabling the efficient exploration of complex potential- and free-energy landscapes, including rare events. These capabilities are combined with a broad hierarchy of energy and force evaluation methods, ranging from classical and machine-learned interaction potentials and mixed quantum-classical multiscale and semiempirical schemes, to highly accurate quantum-mechanical electronic-structure approaches. At the heart of the latter lies the Gaussian and plane-wave framework, along with its augmented all-electron generalization, which have been described in detail in our previous code review [T. D. K\"uhne et al., J. Chem. Phys. 152, 194103 (2020)]. Building on this foundation, the present work revisits the methods within CP2K that turn electronic structure into dynamics, transport, and spectroscopic response. Particular emphasis is placed on the coupling between static response calculations and nuclear motion: spectra may be evaluated at optimized structures, averaged over thermally sampled configurations, obtained from time-correlation functions along ab-initio or path integral molecular trajectories, or followed in real time together with electronic and nuclear dynamics. The same modular structure also enables equilibrium and biased transport simulations, from Kubo-type linear response to open-boundary approaches under external potentials, highlighting CP2K's unique capability to unify quantum chemistry with quantum and statistical mechanics within a versatile, holistic simulation environment.
Jan Wilhelm, Anna-Sophia Hehn, Hossam Elgabarty et al.· 1 citation· ⚡1
Stimulated by the renewed interest and recent developments in semiempirical quantum chemical (SQC) methods for noncovalent interactions, we examine the properties of liquid water under ambient conditions by means of molecular dynamics (MD) simulations, both with the conventional neglect of diatomic differential overlap-type methods, e.g., AM1 and PM6, and with DFTB-type (density-functional tight-binding) methods, e.g., DFTB2 and GFN-xTB (Geometry-Frequency-Noncovalent eXtended Tight-Binding). Besides the original parameter sets, some specifically reparameterized SQC methods (denoted as AM1-W, PM6-fm, and DFTB2-iBi) targeting various smaller water systems ranging from molecular clusters to bulk are considered as well. The quality of these different SQC methods for describing liquid water properties under ambient conditions is assessed by comparison with well-established experimental data and also with BLYP-D3 density functional theory-based ab initio MD simulations. Our analyses reveal that static and dynamic properties of bulk water are poorly described by all considered SQC methods with the original parameters, regardless of the underlying theoretical models, with most of the methods suffering from too weak hydrogen bonds and hence predicting a far too fluid water with highly distorted hydrogen bond kinetics. Meanwhile, the reparameterized force-matched PM6-fm method is shown to be able to quantitatively reproduce the static and dynamic features of liquid water and thus can be used as a computationally efficient alternative to electronic structure-based MD simulations for liquid water that requires extended length and time scales. DFTB2-iBi predicts a slightly overstructured water with reduced fluidity, whereas AM1-W gives an amorphous ice-like structure for water under ambient conditions.
Xin Wu, Hossam Elgabarty, Vahideh Alizadeh et al.· Journal of Chemical Physics· 0 citations