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

The requirement of huge computational resources makes quantum chemical investigations on large molecules prohibitively difficult. In particular, calculating the vibrational IR/Raman spectra of large molecules employing correlated ab initio theory is a herculean task. The present article brings out the utility of our molecular tailoring approach (MTA)-based software for accurate yet economic spectral calculations employing one or more desktop computers. Hartree-Fock and density functional theory-based benchmark calculations on test cases containing over 175 atoms and over 2300 basis functions show excellent agreement with their full calculations (FC) counterparts with large savings in the computer time and memory/hard disk requirements. These savings are even more impressive at MP2 level of theory. Our MTA-based software thus represents an art-of-the-possible for computing vibrational IR/Raman spectra using a handful of desktop machines. SYNOPSIS Ab initio computations of vibrational IR/Raman spectra for large molecular systems are prohibitive due to high scaling complexity and large computational resources required. Fragmentation methods provide an economical avenue for this purpose. This work presents the fragmentation-based MTA software for enabling accurate calculation of molecular energy and vibrational IR/Raman spectra for large molecules employing off-the-shelf hardware. Accuracy and efficacy of software is demonstrated for a variety of large molecules/clusters employing large basis sets with HF-, density functional- and MP2 theory.