Pragmatic Many-Body Approach for Economic MP2 Energy Estimation of Molecular Clusters

Abstract

We propose a procedure, within the many-body analysis (MBA) framework, for an economic yet accurate estimation of the correlated method-based energies of large molecular clusters employing Dunning’s augmented basis sets. The basis of the procedure is to segregate the Hartree–Fock (E HF) and correlation energy (E C) estimations. E HF is found to differ by tens of millihartrees (mH) from its full-calculation (FC) counterpart on truncating the MBA expansion at the two-body (MBA-2) level. On the contrary, E C is estimated with smaller error on modest hardware with limited computation time at the (MBA-2) level. In view of this, we adopt a pragmatic method wherein the E HF (accurate to five decimal places) is taken from the FC, whereas E C is estimated at the MBA-2 level. This method is applied to a variety of medium to large molecular clusters at the MP2 level. Preliminary results at the CCSD­(T) level for (H2O)16 and (H2O)17 are also reported with tremendous savings in wall-clock time and resources. The typical errors in MP2 and CCSD­(T) energies per monomer are up to 0.1 and 0.2 mH, respectively. Thus the present method, balancing accuracy and computational economy, opens a way for estimating energies of large molecular clusters using correlated theories with large basis sets.

Energy-Screened Many-Body Expansion: A Practical Yet Accurate Fragmentation Method for Quantum Chemistry

“…Calculations for small water clusters indicate that electron correlation effects are nearly pairwise-additive; − nevertheless, four- and five-body terms contribute 1–2 kcal/mol to the total interaction energies of clusters ranging from (H 2 O) 6 to (H 2 O) 16 . − In larger water clusters, our own work suggests that four-body terms are necessary to obtain (or even approach) chemical accuracy. ,, This largely remains true even when electrostatic embedding is employed in an effort to capture higher-order polarization effects …”

Molecular Tailoring Approach for the Estimation of Intramolecular Hydrogen Bond Energy

“…The molecular tailoring approach (MTA) is a fragmentation-based technique developed by Gadre et al [ 68 , 69 , 70 , 71 , 72 , 73 , 74 , 75 , 76 , 77 , 78 , 79 , 80 , 81 , 82 ]. Within MTA, a spatially extended molecular system under consideration is partitioned into a set of overlapping fragments (called the “main fragments”) on which ab initio calculations for one-electron property or the energy are carried out.…”

“…Thus, it was felt necessary to come up with a direct theoretical method for a reliable estimation of IHB energy. Deshmukh and Gadre [ 66 , 67 ] proposed such a procedure, based on the in-house developed molecular tailoring approach (MTA) for the ab initio treatment of large molecular systems [ 68 , 69 , 70 , 71 , 72 , 73 , 74 , 75 , 76 , 77 , 78 , 79 , 80 , 81 , 82 ]. The MTA currently enables the calculation of one-electron properties, geometry optimization, and the calculation of vibrational infrared and Raman spectra of large molecules/clusters using DFT or correlated methods.…”

“…This error can be further reduced using the so-called grafting procedure embedded in the current version of MTA [77,78].Gadre et al first proposed the MTA methodology for estimating the electrostatic properties of large, closed-shell molecules[68]. However, in the last 24 years, the scope of MTA was extended for the estimation of molecular energy[69], geometry optimization[70,71], the estimation of the Hessian matrix[72], the computation of vibrational infrared[73] and Raman spectra[74], and binding energies of large molecular clusters and complexes[75][76][77][78][79][80][81][82]. Since the fragment computations are independent of each other, MTA has the advantage that the energy computation of the parent molecule is intrinsically parallel.…”

Development and testing of an algorithm for efficient MP2/CCSD(T) energy estimation of molecular clusters with the 2–body approach

“…This approximation adds the Hartree‐Fock (HF) energy of the entire cluster to the total correlation contribution of all the two‐body interaction energies. They 25,26 found that the molecular energies thus generated are in excellent agreement with the respective MP2/CCSD(T) ‐level energy of the molecular cluster, with an error of 1–2 millihartree (mH) for the clusters studied by them. The test cases chosen by Deshmukh and Sakaki 25 included small‐ and medium‐sized homo/hetero‐trimers.…”