First-Principles Crystal Structure Prediction of Cu(I)-TCNQ Polymorphs

Abstract

There is a lack of consensus on the crystal structure and polymorphism of Cu­(I)-TCNQ, even though an enormous work and great achievements have been reported for decades. This motivated us to perform a crystal structure prediction study [by using the Fast and Flexible CrystAl Structure Predictor (FFCASP)] combined with total energy calculations at the dispersion-corrected density functional theory (DFT-D) level. The ensemble of the optimized structures falls in two distinct regions based on the energy-density phase space. Our predictions located the thermodynamic phase (as a global minimum) and a conformationally similar local minimum structure to the experimentally proposed phase I, in the low- and high-density regions, respectively. The Rietveld refinement of the P21212 local minimum structure to the experimental X-ray diffraction (XRD) pattern resulted in a structure with a density between the two regions. This polymorph, the kinetic product, becomes a high-energy local minimum structure after the full geometry optimization, being 35.03 kJ/mol above the global minimum. In addition, we found that the transition from the high- to the low-density region occurs via square planar coordination of copper atoms.

Adsorption of phosphate by cancrinite in red mud: a first-principles study

“…The total energy of the system is shown in table 1. The smaller the total energy of the system, the more stable the crystal structure [41,42]. When cancrinite adopted the exchange correlation functional GGA-PW91, the system energy was the lowest, that is, the crystal structure was in the most stable state.…”

Crystal Structure Prediction and Dehydrogenation Mechanism of LiMg(BH4)3(NH3)2

“…We used FFCASP, , developed in our group, for the CSP calculations in combination with DFT calculations for full geometry optimization of the candidate structures. Very recently, we successfully applied this methodology to study the polymorphism of Cu-TCNQ .…”

“…We used FFCASP, , developed in our group, for the CSP calculations in combination with DFT calculations for full geometry optimization of the candidate structures. Very recently, we successfully applied this methodology to study the polymorphism of Cu-TCNQ . In FFCASP, we have implemented a hybrid combination of particle swarm optimization (PSO) and simulated annealing (SA) algorithms for the global optimization strategy.…”

“…Moreover, it has been shown that ammonia release is suppressed during the decomposition of LiMg(BH 4 ) 3 (NH 3 ) 2 . 31 These encouraging findings motivated us to perform a more detailed investigation of the polymorphism of LiMg-(BH 4 ) 3 (NH 3 ) 2 and the mechanism of hydrogen release by employing our new CSP tool, called Fast and Flexible CrystAl Structure Predictor (FFCASP) 32 dynamics (CPMD). In addition, phonon calculations helped to verify the dynamical stability of the low-energy structures.…”

“…Very recently, we successfully applied this methodology to study the polymorphism of Cu-TCNQ. 32 In FFCASP, we have implemented a hybrid combination of particle swarm optimization (PSO) 34 and simulated annealing (SA) 35 algorithms for the global optimization strategy. This hybrid implementation is massively parallelized via the task-farming fashion 36 with the message passing interface library, which makes FFCASP perform more trials in the search space during each iteration and consequently allows to increase the success rate.…”