Structures, energetics and vibrational spectra of (H₂O)₃₂clusters: a journey from model potentials to correlated theory

Abstract

Fragmentation details for the W32-TIP4P-Ew isomer. The monomer indices only for the main fragments are listed below. Size indicates the number of water monomers in each main fragment.

Harnessing desktop computers for ab initio calculation of vibrational IR/Raman spectra of large molecules

“…Since the errors in MTA energies are indeed very small (sub millihartree), it is assured that the relative energies of isomers/conformers are well reproduced within MTA, obviating the need of Full calculations. 13 Time advantage for the estimation of vibrational IR/Raman at HF/DFT level is comparatively smaller due to the inherent O(N 3 to N 4 ) scaling. However, in the case of a correlated method, e.g.…”

“…This feature of MTA has been gainfully employed previously for MP2 level calculations on large water clusters. 13 With a larger number of computational nodes, the performance of MTA to enable vibrational IR/Raman spectra of large systems is also expected to grow substantially. It is envisaged that with MTA running on a dozen multi-core computers, the calculations of vibrational IR/Raman spectra for spatially extended molecular systems containing ∼500 atoms would be readily possible in the years to come.…”

“…polarizability-derivative tensors are generated and used for calculating IR/Raman intensities respectively. 12,13 For all the test cases, fragmentation is done manually by the use of visualization software MeTAStudio. 19 However, for the uninitiated user, the utility for automatic generation of fragmentation scheme is also available.…”

“…[8][9][10][11] However, the accuracy and efficiency of DF, RI and local methods need to be carefully benchmarked, especially for the calculation of the spectral properties. On account of simplicity in execution, ease in parallelization and high accuracy, 12,13 fragment-based methods have gained popularity over the last decade. Nevertheless, it should be borne in mind that all such routes are approximations to canonical full calculations (FC) which demand huge computational resources.…”

“…In the present work, we demonstrate our home-built molecular tailoring approach (MTA)-based software showcasing the calculations of energies and vibrational (within harmonic approximation) IR/Raman spectra of large molecules employing a multi-core desktop machine. Details of MTA have been given in the earlier publications from our group, 12,13 but a brief summary of MTA is given for the uninitiated reader in the following section.…”