PNOF5 calculations based on the “thermodynamic fragment energy method”: C n H2n+2 (n = 1, 10) and (FH) n (n = 1, 8) as test cases

Xabier Lopez,Mario Piris

doi:10.1007/s00214-015-1756-x

Abstract

The performance of the “thermodynamic fragment energy method” (FEM) in the context of natural orbital functional theory (NOFT) in its PNOF5 implementation is assessed. Two test cases are considered: the linear chains C n H2n+2 (n = 1, 10) and the hydrogen-bonded (FH) n (n = 1, 8) clusters. Calculations show a fast convergence of the PNOF5-FEM method, which allows the treatment of extended system at a fractional cost of the whole calculation. We show that this type of methodologies could expand the range of systems achievable by NOFT due to the significant reduction in the computational cost.

Highlights

In the last decade, a series of functionals has been developed [1, 2] using a reconstruction proposed by Piris [3] of the two-particle reduced density matrix (2-RDM) in terms of the one-particle RDM (1-RDM)
For the (FH)n clusters, we first optimized the (FH)8 cluster, and the rest of geometries were taken by deleting FH units, to prevent the collapse of the cluster of lower size to geometries other than zigzag ones
All Piris natural orbital functional 5 (PNOF5) calculations have been carried out using our computational code DoNOF with the 6-31G and 6-31G(d,p) basis set [38] and the correlation-consistent valence double-ζ developed by Dunning et al [39]

Summary

Introduction

A series of functionals has been developed [1, 2] using a reconstruction proposed by Piris [3] of the two-particle reduced density matrix (2-RDM) in terms of the one-particle RDM (1-RDM). IKERBASQUE, Basque Foundation for Science, 48013 Bilbao, Euskadi, Spain be comparable to accurate quantum chemistry methods in many cases [4,5,6,7,8,9,10,11,12,13,14,15,16,17,18]. This is the only natural orbital functional (NOF) that has been obtained by top-down and bottom-up methods [19]. In the case of PNOF5, this wavefunction is an antisymmetrized product of strongly orthogonal geminals (APSGs), with the expansion coefficients explicitly expressed by the occupation numbers [20, 21]

Objectives

Methods

Results

Conclusion