AgusRifani (2010) Studi struktur dan sifat elektronik kristal na, mg, al, si dan ar dengan pendekatan teori fungsional kerapatan. Sarjana thesis, Universitas Brawijaya.
Abstract
Kestabilan kristal pada kondisi yang sulit dicapai eksperimen dapat diprediksi melalui metode komputasi. Meskipun demikian, terdapat banyak kemungkinan struktur stabil yang harus dihitung. Jumlah kemungkinan struktur stabil dapat diperkecil jika diketahui ciri dalam sifat elektronik yang menandakan kestabilan struktur tersebut. Dengan demikian perlu dicari keterkaitan antara sifat struktur stabil dan sifat elektronik. Sifat struktur dan sifat elektronik telah dihitung pada kristal elemental Na, Mg, Al, Si dan Ar dalam struktur cF8, cI2, cF4, dan hP2 dengan menggunakan teori fungsional kerapatan. Fungsional exchange-correlation didapat melalui hampiran kerapatan lokal. Efek inti-ion digantikan oleh potensial semu Troullier-Martin, di mana elektron di kelopak ketiga dianggap sebagai elektron valensi. Fungsi gelombang diekspansi dalam planeweve basis-set. Akurasi perhitungan diatur melalui jumlah sampling k-point dan jumlah basis-set planewave. Hasil perhitungan menunjukkan bahwa kristal Na, Mg, Al, Si, dan Ar pada T=0 K memiliki kestabilan dalam struktur, berturut-turut, hP2, hP2, cF4, cF8, dan cF4, sesuai dengan data eksperimen. Perhitungan tekanan transisi tidak menunjukkan kesesuaian dengan data eksperimen karena pengaruh yang berbeda dari suku pV tiap struktur. Konstanta kekisi dapat dihitung dengan perbedaan relatif sekitar 2% untuk kristal kubik dan 6% untuk kristal heksagonal. Pada volume unit sel yang lebih kecil dari volume setimbang, kristal elemental cenderung mengambil struktur dengan bilangan koordinasi yang lebih tinggi. Kestabilan relatif kristal Na, Mg, dan Al dicirikan dengan terbentuknya pseudogap di tingkat energi Fermi.
English Abstract
Crystal stability at the condition that difficult to achieve experimentally can be predicted by means of computational method. However, there is too much possibility of stable structure that should be calculated. The number of possible structure can be reduced if the character of stable structure from electronic properties is known. Therefore, the relationship between the properties of stable structure and electronic properties is needed to identify. The structure and electronic properties of elemental crystal Na, Mg, Al, Si, and Ar in the cF8, cI2, cF4, and hP2 structure have been calculated by using density functional theory. Exchange-correlation functional is used by applying local density approximation. The ion-core effect is replaced by Troullier-Martin pseudopotential in which the third shell electrons is treated as valence electrons. The electronic wavefunction expanded in the planewave basis set. The accuracy of calculation is tuned by the number of k-point sampling and planewave basis set. The result show that, in T=0 K, the stable structure of Na, Mg, Al, Si, and Ar is, respectively, hP2, hP2, cF4, cF8, and cF4, which is in agreement with experimental observation. The calculated phase transition pressure has no accordance with experimental data mainly caused by different effect of pV term in different structure. Lattice constant can be calculated by relative difference to experimental data about 2% for cubic crystal and 6% for hexagonal crystal. In the unit cell volume that smaller than the equilibrium volume, elemental crystal have a propensity to the structure with higher coordination number. The relative stability of crystalline Na, Mg, and Al are characterized by pseudogap at the Fermi energy level.
| Item Type: | Thesis (Sarjana) |
|---|---|
| Identification Number: | SKR/MIPA/2010/58/0510006616 |
| Subjects: | 500 Natural sciences and mathematics > 530 Physics |
| Divisions: | Fakultas Matematika dan Ilmu Pengetahuan Alam > Fisika |
| Depositing User: | Unnamed user with email repository.ub@ub.ac.id |
| Date Deposited: | 15 Mar 2010 10:50 |
| Last Modified: | 22 Oct 2021 06:57 |
| URI: | http://repository.ub.ac.id/id/eprint/152519 |
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