arXiv subjects

Andrew M. Sand

Publications and source records attributed to Andrew M. Sand.

3 recordsLinked to original sources

arXiv2026

Exploring electron transport in carbon wire systems using a wave function-based multiconfigurational non-equilibrium Green's function approach

One-dimensional carbon wire materials are an interesting class of materials which have potentially useful applications in sub-nanoscale junction technology due to their unique quantum transport properties. In this work, we apply a non-equilibrium Green's function approach based on multiconfiguration pair-density functional theory (NEGF-MCPDFT). NEGF-MCPDFT is a wave-function-based non-periodic framework to study electron transport in systems exhibiting strong correlation. The advantage of this approach is multiconfigurational wave functions are used which offer enhanced abilities to describe strong electron correlation beyond single-determinant approaches. MC-PDFT necessitates the use of an active space, and a key step in such calculations is the determination of which orbitals to include. In application of this theory to carbon wire junctions of various lengths, we find that NEGF-MCPDFT is capable of reproducing trends from recent experimental results, and we use our findings to further the development of best practices in active space design for transport calculations of this type.

physics.chem-ph↗

arXiv2021

A multiconfigurational pair-density functional theory approach to molecular junctions

Due to their small size and unique properties, single-molecule electronics have long seen research interest from experimentalists and theoreticians alike. From a theoretical standpoint, modeling these systems using electronic structure theory can be difficult due to the importance of electron correlation in the determination of molecular properties, and this electron correlation can be computationally expensive to consider, particularly multiconfigurational correlation energy. In this work, we develop a new approach for the study of single-molecule electronic systems, denoted NEGF-MCPDFT, which combines multiconfiguration pair-density functional theory (MC-PDFT) with the non-equilibrium Green's function formalism (NEGF). The use of MC-PDFT with NEGF allows for the efficient inclusion of both static and dynamic electron correlation in the description of the junction's electronic structure. CASSCF wave functions are used as references in the MC-PDFT calculation, and like with any active space method, effort must be made to determine the proper orbital character to include in the active space. We perform conductance and transmission calculations on a series of alkanes (predominantly single-configurational character) and benzyne (multiconfigurational character), exploring the role that active space selection has on the computed results. For the alkane junctions explored (where dynamic electron correlation dominates), the MCPDFT-NEGF results agree well with DFT-NEGF results. For the benzyne junction (which has significant static correlation), we see clear differences in the MCPDFT-NEGF and DFT-NEGF results, and evidence that NEGF-MCPDFT is capturing additional electron correlation effects beyond those provided by the PBE functional.

physics.chem-ph↗

arXiv2017

Analytic Gradients for Complete Active Space Pair-Density Functional Theory

Analytic gradient routines are a desirable feature for quantum mechanical methods, allowing for efficient determination of equilibrium and transition state structures and several other molecular properties. In this work, we present analytical gradients for multiconfiguration pair-density functional theory (MC-PDFT) when used with a state-specific complete active space self-consistent field reference wave function. Our approach constructs a Lagrangian that is variational in all wave function parameters. We find that MC-PDFT locates equilibrium geometries for several small- to medium-sized organic molecules that are similar to those located by complete active space second-order perturbation theory but that are obtained with decreased computational cost.

physics.chem-ph↗