First-Principles Magnetic Anisotropy and Statistical-Mechanical Prediction of Magnetic Alignment in Aromatic PET-Type Polymer Domains
- 1School of Chemistry
- 2Indian Institute of Science Education and Research Thiruvananthapuram
Abstract
Gauge-including-atomic-orbital (GIAO) density functional theory calculations at the B3LYP/6-31+G(d,p) level are used to determine the molecular magnetic susceptibility tensors of a hydroxyl-terminated poly(ethylene terephthalate) (PET) oligomer series - PET1/BHET, PET2, and PET3 - and the results are carried through an explicit statistical-mechanical model of field-induced domain alignment. The isotropic molecular response becomes increasingly negative with oligomer length, while the chemically defined axial anisotropy along the terephthalate backbone remains approximately constant at 15–16 atomic units, showing that total diamagnetic response and magnetic anisotropy are governed by distinct structural features. A continuum orientational model based on the ratio λ = VΔχB2/(2μ0kBT) of magnetic to thermal energy is used to obtain the exact Boltzmann orientational distribution and the second-rank order parameter S, together with an overdamped-rotation estimate of the characteristic alignment time. Because a molecular susceptibility tensor is not automatically a bulk volume susceptibility, the continuum values reported here are explicitly identified as provisional, density-based phenomenological estimates rather than validated bulk quantities. The central physical result is that the coherently rotating domain volume, through its cubic scaling of the magnetic energy, dominates the alignment behaviour far more strongly than the modest variation in molecular anisotropy across the oligomer series, so that the crossover field for a given domain scales as B ∝ a-3⁄2. The framework separates a complete first-principles molecular-response and statistical-mechanics treatment from a deliberately provisional molecular-to-bulk conversion, and it identifies the specific calculations — conformer sampling, a structural-axis re-analysis for PET3, a method-sensitivity benchmark, and a validated coarse-graining scheme — required before the predicted alignment fields and order parameters can be compared quantitatively with experiment.
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BibTeX
@misc{roy2026firstprinciples,
title = {{First-Principles Magnetic Anisotropy and Statistical-Mechanical Prediction of Magnetic Alignment in Aromatic PET-Type Polymer Domains}},
author = {Dibakar Roy},
howpublished = {ChemRxiv},
year = {2026},
month = sep,
doi = {10.26434/chemrxiv.15009556/v1},
url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15009556/v1},
note = {CC BY},
}
RIS
TY - UNPB
TI - First-Principles Magnetic Anisotropy and Statistical-Mechanical Prediction of Magnetic Alignment in Aromatic PET-Type Polymer Domains
AU - Dibakar Roy
PY - 2026
DA - 2026/09/28
PB - ChemRxiv
DO - 10.26434/chemrxiv.15009556/v1
UR - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15009556/v1
AB - Gauge-including-atomic-orbital (GIAO) density functional theory calculations at the B3LYP/6-31+G(d,p) level are used to determine the molecular magnetic susceptibility tensors of a hydroxyl-terminated poly(ethylene terephthalate) (PET) oligomer series - PET1/BHET, PET2, and PET3 - and the results are carried through an explicit statistical-mechanical model of field-induced domain alignment. The isotropic molecular response becomes increasingly negative with oligomer length, while the chemically defined axial anisotropy along the terephthalate backbone remains approximately constant at 15–16 atomic units, showing that total diamagnetic response and magnetic anisotropy are governed by distinct structural features. A continuum orientational model based on the ratio λ = VΔχB2/(2μ0kBT) of magnetic to thermal energy is used to obtain the exact Boltzmann orientational distribution and the second-rank order parameter S, together with an overdamped-rotation estimate of the characteristic alignment time. Because a molecular susceptibility tensor is not automatically a bulk volume susceptibility, the continuum values reported here are explicitly identified as provisional, density-based phenomenological estimates rather than validated bulk quantities. The central physical result is that the coherently rotating domain volume, through its cubic scaling of the magnetic energy, dominates the alignment behaviour far more strongly than the modest variation in molecular anisotropy across the oligomer series, so that the crossover field for a given domain scales as B ∝ a-3⁄2. The framework separates a complete first-principles molecular-response and statistical-mechanics treatment from a deliberately provisional molecular-to-bulk conversion, and it identifies the specific calculations — conformer sampling, a structural-axis re-analysis for PET3, a method-sensitivity benchmark, and a validated coarse-graining scheme — required before the predicted alignment fields and order parameters can be compared quantitatively with experiment.
ER -