• Title, Summary, Keyword: DFT

Search Result 961, Processing Time 0.05 seconds

A Comparison of the Density Functional Theory Based Methodologies for the Triplet Excited State of 𝛑-Conjugated Molecules: Time-Dependent DFT (TD-DFT), TD-DFT within Tamm-Dancoff Approximation (TDA-DFT), and Spin-Unrestricted DFT (UDFT) (𝛑-공액계 분자의 삼중항 여기 상태에 대한 Density Functional Theory (DFT)에 기반한 계산 방법들의 비교: 시간-의존 DFT (TD-DFT), Tamm-Dancoff 근사법을 적용한 DFT (TDA-DFT), 스핀-비제한 DFT (UDFT))

  • Ahn, Chang Hwan;Kim, Dongwook
    • Journal of the Korean Chemical Society
    • /
    • v.63 no.2
    • /
    • pp.73-77
    • /
    • 2019
  • We compared methodologies based on the density functional theory (DFT), e.g., time-dependent DFT (TD-DFT), TD-DFT within Tamm-Dancoff approximation (TDA-DFT), and spin-unrestricted DFT (UDFT), that are usually employed to optimize the geometries of ${\pi}$-conjugated molecules in their lowest lying triplet excited ($T_1$) state. As a model system for ${\pi}$-conjugated molecules, we employed 1,2,3,4,5-pentacyano-6-phenyl-benzene. In conjunction with 6-31G(d) basis sets, we made use of gap-tuned range-separated ${\omega}B97X$ functional which is often employed recently in the calculations of molecular excited states. Near the equilibrium geometries, we found that the important difference between the geometries derived at UDFT level and those at TD-DFT or TDA-DFT methods: more stable ground-state energies but higher triplet excitation energies for UDFT derived geometries. In the studies, we discuss such differences in more detail.

Comparison of Time and Frequency Resources of DFT-s-OFDM Systems Using the Zero-Tail and Unique Word (Zero Tail과 Unique Word를 사용하는 DFT-s-OFDM 시스템들의 시간과 주파수 자원 비교)

  • Kim, Byeongjae;Ryu, Heung-Gyoon
    • The Journal of Korean Institute of Communications and Information Sciences
    • /
    • v.41 no.12
    • /
    • pp.1715-1720
    • /
    • 2016
  • In the upcoming 5-generation mobile communication system, various techniques for improving the power efficiency and spectral efficiency have been proposed. 5G mobile communication system also have been studied a lot of multi-carrier-based modulation techniques like the 4G mobile communication system. In this paper, we analyzed the conventional system structure of the Zero-tail DFT-s-OFDM and UW (Unique Word) -DFT-s-OFDM system based on DFT-s-OFDM system in these techniques. UW and zero are added and used each system, and CP is removed. the result of quality of systems for simulation, OOB(Out of Band) power of Zero-tail DFT-s-OFDM and UW-DFT-s-OFDM use the less time resource as long as CP length, also both systems are reduced about 11dB than DFT-s-OFDM system. In these result, Zero-tail DFT-s-OFDM and UW-DFT-s-OFDM system are more effective than DFT-s-OFDM system.

PAPR Evaluation and Analysis of Candidate Waveforms Using DFT Spreading for 5G Mobile Communications (DFT Spreading을 사용한 5세대 이동통신 후보 변조기술의 PAPR 평가 및 분석)

  • An, Changyoung;Ryu, Heung-Gyoon
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
    • /
    • v.26 no.12
    • /
    • pp.1091-1099
    • /
    • 2015
  • UFMC(Universal-Filtered Multi-carrier) and FBMC(Filter Bank Multi-carrier) system are receiving attention as candidate waveforms for 5G mobile communication system. But, these systems have high PAPR(Peak to Average Power Ratio) problem because these systems use a number of subcarrier. In this paper, we propose DFT(Discrete Fourier Transform) spreading based DFT-s(spreading)-UFMC system and DFT-s-FBMC system in order to overcome the PAPR drawback. In order to evaluate PAPR performance of the proposed systems, we design and simulate OFDM(Orthogonal Frequency Division Multiplexing), UFMC, FBMC, DFT-s-OFDM, DFT-s-UFMC, DFT-s-FBMC system. As simulation results, each PAPR performance of DFT-s-OFDM system, DFT-s-UFMC system, and DFT-s-FBMC system rise by 2.7 dB, 2.8 dB, and 1.1 dB respectively by DFT spreading technique.

Privacy-Preserving Clustering on Time-Series Data Using Fourier Magnitudes (시계열 데이타 클러스터링에서 푸리에 진폭 기반의 프라이버시 보호)

  • Kim, Hea-Suk;Moon, Yang-Sae
    • Journal of KIISE:Databases
    • /
    • v.35 no.6
    • /
    • pp.481-494
    • /
    • 2008
  • In this paper we propose Fourier magnitudes based privacy preserving clustering on time-series data. The previous privacy-preserving method, called DFT coefficient method, has a critical problem in privacy-preservation itself since the original time-series data may be reconstructed from privacy-preserved data. In contrast, the proposed DFT magnitude method has an excellent characteristic that reconstructing the original data is almost impossible since it uses only DFT magnitudes except DFT phases. In this paper, we first explain why the reconstruction is easy in the DFT coefficient method, and why it is difficult in the DFT magnitude method. We then propose a notion of distance-order preservation which can be used both in estimating clustering accuracy and in selecting DFT magnitudes. Degree of distance-order preservation means how many time-series preserve their relative distance orders before and after privacy-preserving. Using this degree of distance-order preservation we present greedy strategies for selecting magnitudes in the DFT magnitude method. That is, those greedy strategies select DFT magnitudes to maximize the degree of distance-order preservation, and eventually we can achieve the relatively high clustering accuracy in the DFT magnitude method. Finally, we empirically show that the degree of distance-order preservation is an excellent measure that well reflects the clustering accuracy. In addition, experimental results show that our greedy strategies of the DFT magnitude method are comparable with the DFT coefficient method in the clustering accuracy. These results indicate that, compared with the DFT coefficient method, our DFT magnitude method provides the excellent degree of privacy-preservation as well as the comparable clustering accuracy.

BER Performance Comparison and Evaluation of 5G Candidate Waveforms Based on DFT Spreading under the Nonlinear HPA (비선형 HPA 환경에서 DFT Spreading 기반 5세대 후보변조기술의 BER 성능 비교와 평가)

  • An, Changyoung;Ryu, Heung-Gyoon
    • The Journal of Korean Institute of Communications and Information Sciences
    • /
    • v.41 no.4
    • /
    • pp.415-423
    • /
    • 2016
  • High PAPR (Peak-to-Average Power Ratio) characteristic causes some problems like system performance degradation and OOB (Out-of-Band) power increasement under the HPA (High Power Amplifier) nonlinearity condition. UFMC (Universal Filtered Multi-Carrier) and FBMC (Filter Bank Multi-Carrier) are regarded as 5G(Generation) candidate waveforms. In this paper, we evaluate and analyze performance of these systems with DFT-s (Discrete Fourier Transform Spreading) technique under the nonlinear HPA environment. In this paper, we describe OFDM (Orthogonal Frequency Division Multiplexing), UFMC, FBMC, DFT-s-OFDM, DFT-s-UFMC, and DFT-s-FBMC system, and evaluate BER (Bit Error Rate) performance of these systems. As simulation results, BER performance degradation by HPA nonlinearity of DFT-s-OFDM and DFT-s-UFMC is greatly overcome by DFT spreading technique. However, BER performance degradation by HPA nonlinearity of DFT-s-FBMC system is little overcome.

A New Sparse Matrix Analysis of DFT Similar to Element Inverse Jacket Transform (엘레멘트 인버스 재킷 변환과 유사한 DFT의 새로운 희소 행렬 분해)

  • Lee, Kwang-Jae;Park, Dae-Chul;Lee, Moon-Ho;Choi, Seung-Je
    • The Journal of Korean Institute of Communications and Information Sciences
    • /
    • v.32 no.4C
    • /
    • pp.440-446
    • /
    • 2007
  • This paper addresses a new representation of DFT matrix via the Jacket transform based on the element inverse processing. We simply represent the inverse of the DFT matrix following on the factorization way of the Jacket transform, and the results show that the inverse of DFT matrix is only simply related to its sparse matrix and the permutations. The decomposed DFT matrix via Jacket matrix has a strong geometric structure that exhibits a block modulating property. This means that the DFT matrix decomposed via the Jacket matrix can be interpreted as a block modulating process.

Dissociation Curves of diatomic molecules and anions: A DC-DFT Study (밀도교정 밀도범함수를 이용한 이원자분자의 해리곡선 연구)

  • Go, Dong-Hyeok;Park, Han-Sol;Kim, Min-Cheol;Sim, Eun-Ji
    • Proceeding of EDISON Challenge
    • /
    • /
    • pp.115-125
    • /
    • 2014
  • We investigate dissociation of diatomic molecules and anions using density functional theory (DFT) and density-corrected density functional theory (DC-DFT). We scan the potential energy curve of CH, NH and NO neutral molecule and its anion with both DFT and DC-DFT (in form of Hartree-Fock DFT, HF-DFT) using various functionals. Using CCSD(T) results as reference, we perform the error decomposition scheme recently proposed by Kim et al. The results show while most neutrals are $functio{\acute{n}}al$ error $domi{\bar{n}}ating$ normal calculations, $CH^-$ and $NO^-$ anions are density-driven error dominating abnormal calculations. In case of $NH^-$, traditional DFT goes to a wrong dissociation limit indicating abnormality, but both HF-DFT and CCSD(T) results need further investigation due to the kinks on the curve.

  • PDF

Variance Distributions of the DFT and CDFT (DFT와 CDFT의 분산 분포)

  • 최태영
    • Journal of the Korean Institute of Telematics and Electronics
    • /
    • v.21 no.4
    • /
    • pp.7-12
    • /
    • 1984
  • A composite - discrete courier transform (CDFT) is developed, which can diagonalize a real symmetric circulant matrix. In general the circulant matrices can be diagonalized by the discrete Fourier transform (DFT). With the analysis of the variance distributions of the DFT and CDFT for the general symmetric covariance matrix of real signals, the DFT and CDFT are compared with respect to the rate distortion performance measure. The results show that the CDFT is more efficient than the DFT in bit rate reduction. In addition, for a particular 64$\times$64 points covariance matrix (f(q)=(0.95)q), the amount of the relative average bit rate reduction for the CDFT with respect to the DFT is obtained by 0.0095 bit with a numerical calculation.

  • PDF

Efficient DFT/DCT Computation for OFDM in Cognitive Radio System (Cognitive Radio 시스템의 OFDM을 위한 효율적 DCT/DFT 계산에 관한 연구)

  • Chen, Zhu;Kim, Jeong-Ki;Yan, Yi-Er;Lee, Moon-Ho
    • Journal of the Institute of Electronics Engineers of Korea TC
    • /
    • v.45 no.2
    • /
    • pp.97-102
    • /
    • 2008
  • In this paper, we address the OFDM based on DFT or DCT in Cognitive Radio system. An adaptive OFDM based on DFT or DCT in Cognitive Radio system has the capacity to nullify individual carriers to avoid interference to the licensed users. Therefore, there could be a considerably large number of zero-valued inputs/outputs for the IDFT/DFT or IDCT/DCT on the OFDM transceiver. Hence, the standard methods of DFT and DCT are no longer efficient due to the wasted operations on zero. Based on this observation, we present a transform decomposition on two dimensional(2-D) systolic array for IDFT/DFT and IDCT/DCT, this algorithm can achieve an efficient computation for OFDM in Cognitive Radio system

DCT/DFT Hybrid Architecture Algorithm Via Recursive Factorization (순환 행렬 분해에 의한 DCT/DFT 하이브리드 구조 알고리듬)

  • Park, Dae-Chul
    • Journal of the Institute of Convergence Signal Processing
    • /
    • v.8 no.2
    • /
    • pp.106-112
    • /
    • 2007
  • This paper proposes a hybrid architecture algorithm for fast computation of DCT and DFT via recursive factorization. Recursive factorization of DCT-II and DFT transform matrix leads to a similar architectural structure so that common architectural base may be used by simply adding a switching device. Linking between two transforms was derived based on matrix recursion formula. Hybrid acrchitectural design for DCT and DFT matrix decomposition were derived using the generation matrix and the trigonometric identities and relations. Data flow diagram for high-speed architecture of Cooley-Tukey type was drawn to accommodate DCT/DFT hybrid architecture. From this data flow diagram computational complexity is comparable to that of the fast DCT algorithms for moderate size of N. Further investigation is needed for multi-mode operation use of FFT architecture in other orthogonal transform computation.

  • PDF