Geri Dön

Anharmonic free energy calculation of dynamically unstable crystalstructures

Başlık çevirisi mevcut değil.

PDF İndir

  1. Tez No: 840464
  2. Yazar: ÇAĞLAYAN ARAS
  3. Danışmanlar: PROF. DR. JOCHEN M. SCHNEİDER, PROF. DR. JÖRG NEUGEBAUER, DR. MORİTZ TO BABEN
  4. Tez Türü: Yüksek Lisans
  5. Konular: Kimya Mühendisliği, Chemical Engineering
  6. Anahtar Kelimeler: Belirtilmemiş.
  7. Yıl: 2021
  8. Dil: İngilizce
  9. Üniversite: Rheinisch-Westfälische Technische Hochschule Aachen
  10. Enstitü: Yurtdışı Enstitü
  11. Ana Bilim Dalı: Belirtilmemiş.
  12. Bilim Dalı: Belirtilmemiş.
  13. Sayfa Sayısı: 58

Özet

The Calphad method is a crucial tool for materials and industrial process design. Success of the method relies heavily on the quality of the materials data and preparation of the datasets requires a detailed and careful study. In this thesis, computational methods that calculate the finite temperature free energies of crystal structures are introduced and implemented on different phases of elements such as Ca, Ti, Zr, Al and Cu. The well known quasi-harmonic model cannot be applied to mechanically unstable phases such as BCC Al-Cu solution or BCC Ti because of the observed imaginary phonon frequencies. For such kind of phases, soft phonon modes are stabilized by selecting a value of finite displacement that is comparable to the desired temperature. Force constants obtained from such displacements are then used in the reference state of the Thermodynamic Integration (TI) method and anharmonic free energies are approximated. A detailed derivation of thermodynamic integration is provided in order to show the possible pitfalls to the reader. If the true form of the Gibbs free energy curve is known, heat capacity can be easily derived. However, small deviations in the free energy can lead to erroneous results. In addition to thermodynamic integration, alternative statistical models that estimate the pressure and volume dependent anharmonic heat capacities are presented. Unary datasets are the foundation of many multi-component databases and require a critical assessment. Among these, a special attention should be given to energetically unfavourable end-members due to the limited amount of experimental data available. In literature, there exist two distinct heat capacity measurements for pure BCC Calcium. Grabowski et al. (2011) have already shown that the SGTE (Scientific Group Thermodata Europe) unary dataset is not the best selection according to DFT calculations. In this study, this is verified by using empirical potentials. At elevated temperatures, BCC Al-Cu solution is stable at around ∼60-80 at.% Cu. In addition to the unary systems, it is also shown that for the Al-Cu system, the BCC solid solution phase is more stable than the FCC phase at elevated temperatures.

Özet (Çeviri)

Özet çevirisi mevcut değil.

Benzer Tezler

  1. Tez No

    232310

    Sülfon ve sülfonamid gruplu moleküllerin konformasyonlarının ve titreşim enerjilerinin kuantum kimyasal yöntemler ile incelenmesi

    Investigations of conformations and vibrational energies of sulfones and sulfonamides by quantum chemical methods

    GÜLCE ÖĞRÜÇ ILDIZ

    Doktora

    Türkçe

    Türkçe

    2008

    Fizik ve Fizik Mühendisliğiİstanbul Üniversitesi

    Fizik Ana Bilim Dalı

    PROF. DR. AYŞEN E. ÖZEL

    PROF. DR. SEVİM AKYÜZ

  2. Tez No

    252814

    Fenazopridin molekülünün konformasyon analizi ve ab-initio DFT yöntemleri ile titreşim frekans ve kiplerinin incelenmesi

    Conformational analysis and ab-initio, DFT studies of vibrational frequencies and modes of phenazopyridine molecule

    YELİZ GÖREN

    Yüksek Lisans

    Türkçe

    Türkçe

    2009

    Fizik ve Fizik Mühendisliğiİstanbul Üniversitesi

    Fizik Ana Bilim Dalı

    DOÇ. DR. YASEMİN AKKAYA

  3. Tez No

    46157

    ^.fazgeçiti yakınında NH4 Br ve NH4CI'ün kritik davranışının incelenmesi

    Analysis of critical behaviour of NH4 Br and NH4CI near ^. point

    TAMER DEMİR

    Yüksek Lisans

    Türkçe

    Türkçe

    1995

    Fizik ve Fizik Mühendisliğiİstanbul Teknik Üniversitesi

    PROF.DR. HAMİT YURTSEVEN

  4. Tez No

    255343

    Density functional theory for trapped ultracold fermions

    Tuzaklanmış ultrasoğuk fermiyonlar için yoğunluk fonksiyoneli teorisi

    ÖZGE AKYAR

    Yüksek Lisans

    İngilizce

    İngilizce

    2009

    Fizik ve Fizik MühendisliğiOrta Doğu Teknik Üniversitesi

    Fizik Ana Bilim Dalı

    YRD. DOÇ. DR. HANDE TOFFOLİ

  5. Tez No

    75622

    Hypervirial analysis of endosed quantum mechanical systems

    Kapalı kuantum mekanik sistemlerinin hypervirial analizi

    ÖMÜR UĞUR

    Yüksek Lisans

    İngilizce

    İngilizce

    1998

    MatematikOrta Doğu Teknik Üniversitesi

    Matematik Ana Bilim Dalı

    PROF. DR. HASAN TAŞELİ

Geri Dön