Optimal cloud use of quartic force fields: The first purely commercial cloud computing based study for rovibrational analysis of SiCH⁻

Abstract

Commercial cloud computing (CCC) has the promise of an untold number of computing nodes available for the researcher as long as he or she has the financial means to absorb these costs and the administrative skills necessary to effectively utilize the resources. The key is finding how to maximize parallelization for a minimum of monetary and management costs. Previous work has shown that CCC resources are viable for use on large numbers of small-to-medium sized quantum chemical computations. Composite energy quartic force fields (QFFs) are a highly-attractive platform for subsequent testing of CCC resources to find the proper balance between time savings of the cloud versus monetary expenditure. Use of this type of potential energy surface has lead to highly-accurate rovibrational data in earlier work. QFFs use large numbers of stand-alone energies that have to be computed for various molecular geometries. At each geometry, different methods and/or basis sets are used to efficiently generate accurate representations of the nuclear potential. For this initial study, the small molecular anion, SiCH 2 of interest in astrochemistry, is chosen for analysis as it can be done cheaply on the cloud while still providing insight into the nature of CCC usage. Additionally, no rovibrational data exists for this molecule making it the first molecule quantum chemically computed purely via CCC tools.

On the Detectability of the HSS, HSO, and HOS Radicals in the Interstellar Medium

“…Utilizing restricted-openshell Hartree-Fock reference wavefunctions Lauderdale et al 1991;Watts et al 1993) for CCSD(T), the geometry is computed with the aug-cc-pV5Z basis set (Dunning 1989; Kendall et al 1992) with the necessary, additional tight d functions for sulfur (Wilson & Dunning 2004) as well as the Martin-Taylor (MT) core correlating basis set (Martin & Taylor 1994) inclusive and exclusive of core electrons correlated. The difference in the MT bond lengths and bond angle are added to the CCSD(T)/aug-cc-pV5Z geometry as has been done for many related systems (Fortenberry et al 2014b;Fortenberry & Francisco 2015a, 2015bFortenberry & Lukemire 2015;Fortenberry & Thackston 2015;Finney et al 2016;Kitchens & Fortenberry 2016).…”

Quantum astrochemical spectroscopy

“…[128] If one job only takes 10 min, as an example, it is sensible to put six jobs serially on one node for a setup with a 1 h billing cycle. If the cost is $0.10 per hour per node, six jobs run in serial on a single node will cost $0.10 while six jobs run in parallel will cost $0.60 run on six nodes.…”

“…The CcC QFF rovibrational spectroscopic data for SiCH 2 , a molecule of potential interest to astrochemistry, have already been computed solely using CCC resources. [128] Whenever computations are needed in high volume and quickly, CCC is unmatched in its application to such quantum chemical problems.…”

“…The most notable example is how to string jobs together on a single node that can take full advantage of a billing cycle . If one job only takes 10 min, as an example, it is sensible to put six jobs serially on one node for a setup with a 1 h billing cycle.…”

Energetics, structure, and rovibrational spectroscopic properties of the sulfurous anions SNO− and OSN−

“…Composite energy schemes to describe the QFF surface developed by Lee and Huang at NASA Ames [31][32][33][34] have been able to match experimental fundamental vibrational frequencies to within 1.0 cm −1 of experiment in many cases 33,[35][36][37][38][39] and within 0.03 Å for bond lengths and 10-20 MHz for some experimental Band C-type rotational constants. 33,34,37,40,41 In fact, QFFs have even shown reliability in the provision of rovibrational insights for closed-shell anions, 24,[41][42][43][44][45][46][47] much like SNO − and OSN − , most notably in the interstellar detection of C 5 N − which was based solely on quantum chemical spectroscopic data. 19,48 These same techniques are applied here to the SNO − and OSN − anion isomers in order to offer the community deeper insights into the rotational, vibrational, and rovibrational character of these stable and simple inorganic species.…”