NTChem is a ab initio quantum chemistry software used to calculate the properties of molecules. Functionally, it is more versatile than any other quantum chemical software, performs various kinds of simulations freely, and handles automated exploration of chemical reaction pathway for large molecular systems. NTChem can also be implemented in multi-core parallel-type calculation systems, such as the RIKEN K computer, to enable high-speed and efficient calculations.
In recent years, calculations for large-scale and complicated molecular systems are being performed more and more frequently in fields such as molecular science. Thus, rapid and high-precision calculations are needed, requiring higher-performance computers. In this context, we developed a general-purpose molecular science calculation software called NTChem.
NTChem incorporates numerous quantum chemical calculation methods that cannot be performed in existing programs. In addition, it has an original parallel algorithm that can derive the maximum performance from a multi core super parallel cluster computer such as the K computer. The developed program successfully performed efficient molecular calculations for large molecules that usually take extensive time in conventional quantum chemical calculation programs. The program was also used to rapidly simulate molecular behaviors that are difficult to replicate experimentally.
The team to which Aki Takazaki of the Kobe University’s Graduate School of Science is affiliated is studying the multi-electron transfer of polyoxometalates (POMs).
Research on multi-electron transfer is important for developing energy technologies necessary to realize sustainable energy society. For example, the study of the multi-electron transfer contributes to the significant improvements of metal–air electrochemical cells which are one of the battery cells required for energy storage. The usual positive electrode reaction in a metal–air electrochemical cell is given by formula 1 (two electron mechanism). However, if the reaction proceeds by a four electron transfer mechanism as given in formula 2, high output cell will be realized. Furthermore, the generation of HO2– that erodes the components of the cell can be reduced in the latter reaction 1).
Formula 1 O2 + H2O + 2e–→ OH–+ HO2– (-0.065V)
Formula 2 O2 + 2H2O + 4e– → 4OH– (0.40V)
As multi-electron-transfer reactions such as above examples do not occur spontaneously, the catalysts that mediate the reactions are needed. Aiming at developing such catalysts, the team to which Aki Takazaki is affiliated, has been investigating the origin of the multi electron transfer of POM using the first-principles electronic structure calculations.
POMs are polyacids consisting of heavy-metal oxide. They have the complicated structure and include many heavy metal atoms. The outer shells (shown yellow octahedral) of POM are formed by bonding network of transition metal M and Oxygen O and exhibit a spherical or an oval shape (closed shell). In the shell an oxoanion (XO48-z) of cation X z is enclosed. Due to their complicated and large structure, the calculation takes extensive time to converge. Actually, when we performed the calculation using an ordinary multi core computer and a commercial quantum chemistry software in our laboratory, it needed about a month to complete the calculation. Furthermore, to elucidate the mechanism of the multi-electron transfer reaction, tremendous amounts of calculations regarding various kinds of parameters are needed. Therefore, the research is time consuming and costly.
It is in this context that NTChem began to be used; it is a type of software that specializes in quantum chemical calculations using supercomputers and allows simulations of medium–large molecules like polyoxometalates in a relatively short period. It took about a month to calculate a polyoxometalate with an ordinary computer using existing software but only one day using a supercomputer with NTChem. This increased efficiency greatly contributed to the progress of the research. At present, NTChem is used to investigate the electronic state, structure, and electrochemical behavior of Keggin-type polytungstate ions with the goal of elucidating the origin of multi-electron transfer in such ions observed in electrochemical experiments.
Thanks to the high efficiency of NTChem, currently, Takazaki is nearly arriving at her research goal. A part of her research achievements has been reported in J. Phys. Chem. A 2017, 121, 7684－7689. She described her future endeavors as follows: “I would like to continue my research aiming to design novel polyoxometalates that really catalyze the multi-electron transfer reactions using automated exploration of chemical reaction pathway by NTChem.”
NTChem greatly contributes to the efficiency of calculations with various molecules, particularly giant molecules, for which calculations are generally time consuming. Although this software was developed by RIKEN, it is open and accessible to the public. Furthermore, a seminar on NTChem is being offered, and a system to support the introduction of this tool into research projects has been established.
To fully demonstrate the performance of NTChem, a supercomputer or a workstation with similar specifications is required. However, we hope that the calculation speed of all computers will increase further and that the use of NTChem will widen accordingly.
１) New Material for Next Generation Rechargeable Batteries for Future Society, K. Kanamura, CMC Publishing Co.,Ltd, 2016, Popular Edition, 137-138