129 research outputs found
Electronic Structure and Linear Optical Properties of SrCuOCl Studied from the First Principles Calculation
First-principles calculations with the full-potential linearized augmented
plane-wave (FP-LAPW) method have been performed to investigate detailed
electronic and linear optical properties of SrCuOCl, which is
a classical low-dimensional antiferromagnet (AFM) charge transfer ({\it CT})
insulator. Within the local-spin-density approximation (LSDA) plus the on-site
Coulomb interaction (LADA+) added on Cu 3d orbitals, our calculated band
gap and spin moments are well consistent with the experimental and other
theoretical values. The energy dispersion relation agrees well with the angle
resolved photoemission measurements. Its linear optical properties are
calculated within the electric-dipole approximation. The absorption spectrum is
found to agree well with the experimental result.Comment: 5 pages, 5 figure
On the Dimensionality of Sentence Embeddings
Learning sentence embeddings is a fundamental problem in natural language
processing. While existing research primarily focuses on enhancing the quality
of sentence embeddings, the exploration of sentence embedding dimensions is
limited. Here we present a comprehensive and empirical analysis of the
dimensionality of sentence embeddings. First, we demonstrate that the optimal
dimension of sentence embeddings is usually smaller than the default value.
Subsequently, to compress the dimension of sentence embeddings with minimum
performance degradation, we identify two components contributing to the overall
performance loss: the encoder's performance loss and the pooler's performance
loss. Therefore, we propose a two-step training method for sentence
representation learning models, wherein the encoder and the pooler are
optimized separately to mitigate the overall performance loss in low-dimension
scenarios. Experimental results on seven STS tasks and seven sentence
classification tasks demonstrate that our method significantly improves the
performance of low-dimensional sentence embeddings
First principles investigation of transition-metal doped group-IV semiconductors: RY (R=Cr, Mn, Fe; Y=Si, Ge)
A number of transition-metal (TM) doped group-IV semiconductors,
RY (R=Cr, Mn and Fe; Y=Si, Ge), have been studied by the first
principles calculations. The obtained results show that antiferromagnetic (AFM)
order is energetically more favored than ferromagnetic (FM) order in Cr-doped
Ge and Si with =0.03125 and 0.0625. In 6.25% Fe-doped Ge, FM interaction
dominates in all range of the R-R distances while for Fe-doped Ge at 3.125% and
Fe-doped Si at both concentrations of 3.125% and 6.25%, only in a short R-R
range can the FM states exist. In the Mn-doped case, the RKKY-like mechanism
seems to be suitable for the Ge host matrix, while for the Mn-doped Si, the
short-range AFM interaction competes with the long-range FM interaction. The
different origin of the magnetic orders in these diluted magnetic
semiconductors (DMSs) makes the microscopic mechanism of the ferromagnetism in
the DMSs more complex and attractive.Comment: 14 pages, 2 figures, 6 table
A Closer Look at the Self-Verification Abilities of Large Language Models in Logical Reasoning
Logical reasoning has been an ongoing pursuit in the field of AI. Despite
significant advancements made by large language models (LLMs), they still
struggle with complex logical reasoning problems. To enhance reasoning
performance, one promising direction is scalable oversight, which requires LLMs
to identify their own errors and then improve by themselves. Various
self-verification methods have been proposed in pursuit of this goal.
Nevertheless, whether existing models understand their own errors well is still
under investigation. In this paper, we take a closer look at the
self-verification abilities of LLMs in the context of logical reasoning,
focusing on their ability to identify logical fallacies accurately. We
introduce a dataset, FALLACIES, containing 232 types of reasoning fallacies
categorized in a hierarchical taxonomy. By conducting exhaustive experiments on
FALLACIES, we obtain comprehensive and detailed analyses of a series of models
on their verification abilities. Our main findings suggest that existing LLMs
could struggle to identify fallacious reasoning steps accurately and may fall
short of guaranteeing the validity of self-verification methods. Drawing from
these observations, we offer suggestions for future research and practical
applications of self-verification methods.Comment: work in progres
A Stitch in Time Saves Nine: Detecting and Mitigating Hallucinations of LLMs by Validating Low-Confidence Generation
Recently developed large language models have achieved remarkable success in
generating fluent and coherent text. However, these models often tend to
'hallucinate' which critically hampers their reliability. In this work, we
address this crucial problem and propose an approach that actively detects and
mitigates hallucinations during the generation process. Specifically, we first
identify the candidates of potential hallucination leveraging the model's logit
output values, check their correctness through a validation procedure, mitigate
the detected hallucinations, and then continue with the generation process.
Through extensive experiments with the 'article generation task', we first
demonstrate the individual efficacy of our detection and mitigation techniques.
Specifically, the detection technique achieves a recall of 88% and the
mitigation technique successfully mitigates 57.6% of the correctly detected
hallucinations. Importantly, our mitigation technique does not introduce new
hallucinations even in the case of incorrectly detected hallucinations, i.e.,
false positives. Then, we show that the proposed active detection and
mitigation approach successfully reduces the hallucinations of the GPT-3 model
from 47.5% to 14.5% on average. In summary, our work contributes to improving
the reliability and trustworthiness of large language models, a crucial step en
route to enabling their widespread adoption in real-world applications
Spin-orbit interaction in Au structures of various dimensionalities
Variation of the geometrical and electronic properties of the gold materials
in different dimensions has been investigated by
method, taking into account the spin-orbit (SO) interaction. It is
found that SO effects in different dimensional Au materials depend greatly on
fundamental symmetry and dimensionality. For single walled gold nanotubes
(SWGNTs), SO interaction decreases significantly the conducting channel number
of achiral SWGNT (4, 0), and leads to spin splitting at Fermi level of chiral
SWGNT, indicating that quasi-1D SWGNT can be a good candidate for the
spin-electron devices. Furthermore, our results suggest that cage cluster might
be synthesizable experimentally by taking gold tube structure as parent
material.Comment: 11 pages, 4 figure
Thrust: Adaptively Propels Large Language Models with External Knowledge
Although large-scale pre-trained language models (PTLMs) are shown to encode
rich knowledge in their model parameters, the inherent knowledge in PTLMs can
be opaque or static, making external knowledge necessary. However, the existing
information retrieval techniques could be costly and may even introduce noisy
and sometimes misleading knowledge. To address these challenges, we propose the
instance-level adaptive propulsion of external knowledge (IAPEK), where we only
conduct the retrieval when necessary. To achieve this goal, we propose
measuring whether a PTLM contains enough knowledge to solve an instance with a
novel metric, Thrust, which leverages the representation distribution of a
small number of seen instances. Extensive experiments demonstrate that thrust
is a good measurement of PTLM models' instance-level knowledgeability.
Moreover, we can achieve significantly higher cost-efficiency with the Thrust
score as the retrieval indicator than the naive usage of external knowledge on
88% of the evaluated tasks with 26% average performance improvement. Such
findings shed light on the real-world practice of knowledge-enhanced LMs with a
limited knowledge-seeking budget due to computation latency or costs.Comment: 13 pages, 6 figure
Chain-of-Note: Enhancing Robustness in Retrieval-Augmented Language Models
Retrieval-augmented language models (RALMs) represent a substantial
advancement in the capabilities of large language models, notably in reducing
factual hallucination by leveraging external knowledge sources. However, the
reliability of the retrieved information is not always guaranteed. The
retrieval of irrelevant data can lead to misguided responses, and potentially
causing the model to overlook its inherent knowledge, even when it possesses
adequate information to address the query. Moreover, standard RALMs often
struggle to assess whether they possess adequate knowledge, both intrinsic and
retrieved, to provide an accurate answer. In situations where knowledge is
lacking, these systems should ideally respond with "unknown" when the answer is
unattainable. In response to these challenges, we introduces Chain-of-Noting
(CoN), a novel approach aimed at improving the robustness of RALMs in facing
noisy, irrelevant documents and in handling unknown scenarios. The core idea of
CoN is to generate sequential reading notes for retrieved documents, enabling a
thorough evaluation of their relevance to the given question and integrating
this information to formulate the final answer. We employed ChatGPT to create
training data for CoN, which was subsequently trained on an LLaMa-2 7B model.
Our experiments across four open-domain QA benchmarks show that RALMs equipped
with CoN significantly outperform standard RALMs. Notably, CoN achieves an
average improvement of +7.9 in EM score given entirely noisy retrieved
documents and +10.5 in rejection rates for real-time questions that fall
outside the pre-training knowledge scope.Comment: Preprin
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