Ab initio analýza fází NiSe, CoSe a SnSe2

Tomáš Pozdíšek

Bachelor's thesis

Ab initio analysis of NiSe, CoSe and SnSe2 phases

Abstract:

Cílem této práce je ab initio analýza čistého hexagonálního selenu a fází, které ho obsahují (tj. SnSe2, CoSe, NiSe) a pěti modifikací fáze CoSe s jednou až pěti vakancemi ve struktuře. Rovnovážně mřížkové parametry jsou pro čistý hexagonální Se a = b = 4,513 Å, c = 5,050 Å a pro fáze: SnSe2 a = b = 3,868 Å, c = 7,015 Å; CoSe a = b = 3,608 Å, c = 5,191 Å; NiSe a = b = 3,703 Å, c = 5,220 Å. Pro modifikace fáze CoSe s vakancemi jsou rovnovážné mřížkové parametry následující: CoSeVa1 a = 14,388 Å, b = 7,192 Å, c = 5,195 Å; CoSeVa2 a = 14,333, b = 7,158 Å, c = 5,195 Å; CoSeVa3-a a = 14,292 Å, b = 7,146 Å, c = 5,171 Å; CoSeVa3-b a = 14,572 Å, b = 6,987 Å, c = 5,081 Å; CoSeVa4 a = 14,244 Å, b = 7,071 Å, c = 5,198 Å; CoSeVa5 a = 14,115 Å, b = 7,066 Å, c = 5,195 Å. Na rozdíl od bezdefektního CoSe se u jeho modifikací s vakancemi objevuje magnetické uspořádání, přičemž nejvyšší hodnoty magnetického momentu vztaženého na výpočetní buňku dosahuje modifikace CoSeVa2, a to s 4,013 μ_B na 30 atomů. Tvorná tepla ∆H studovaných fází jsou následující: SnSe2 -34,381 kJ/mol atomů; CoSe -12,743 kJ/mol atomů; NiSe -23,535 kJ/mol atomů. Tvorná tepla modifikací s vakancemi vztažená k prvkům ve standardním stavu jsou: CoSeVa1 -15,717 kJ/mol atomů; CoSeVa2 -17,982 kJ/mol atomů; CoSeVa3-a -20,104 kJ/mol atomů; CoSeVa3-b -20,755 kJ/mol atomů; CoSeVa4 -17,847 kJ/mol atomů; CoSeVa5 -20,944 kJ/mol atomů a průměrná tvorná tepla vakancí ∆H ̅^f (Va) jsou následovná: CoSeVa1 -79,432 kJ/mol Va; CoSeVa2 -65,837 kJ/mol Va; CoSeVa3-a -58,409 kJ/mol Va; CoSeVa3-b -64,700 kJ/mol Va; CoSeVa4 -22,979 kJ/mol Va; CoSeVa5 -31,537 kJ/mol Va.

Abstract:

The objective of this thesis is the ab initio analysis of pure hexagonal selenium and the phases that contain it (i.e. SnSe2, CoSe, NiSe) and five modifications of the CoSe phase with one to five vacancies in the structure. The equilibrium lattice parameters are for pure hexagonal Se a = b = 4.513 Å, c = 5.050 Å and for phases: SnSe2 a = b = 3.868 Å, c = 7.015 Å; CoSe a = b = 3.608 Å, c = 5.191 Å; NiSe a = b = 3.703 Å, c = 5.220 Å. For modifications of the CoSe phase with vacancies, the equilibrium lattice parameters are as follows: CoSeVa1 a = 14.388 Å, b = 7.192 Å, c = 5.195 Å; CoSeVa2 a = 14.333, b = 7.158 Å, c = 5.195 Å; CoSeVa3-a a = 14.292 Å, b = 7.146 Å, c = 5.171 Å; CoSeVa3-b a = 14.572 Å, b = 6.987 Å, c = 5.081 Å; CoSeVa4 a = 14.244 Å, b = 7.071 Å, c = 5.198 Å; CoSeVa5 a = 14.115 Å, b = 7.066 Å, c = 5.195 Å. In contrast to defect-free CoSe, its modifications with vacancies show magnetic arrangement, where the highest value of the magnetic moment related to the computational cell is achieved by the CoSeVa2 modification, with 4.013 μ_B per 30 atoms. The heats of formation of the studied phases ∆H are as follows: SnSe2 -34.381 kJ/mol of atoms; CoSe -12.743 kJ/mol of atoms; NiSe -23.535 kJ/mol of atoms. The heats of formation of modifications with vacancies related to the elements in the standard state are: CoSeVa1 -15.717 kJ/mol of atoms; CoSeVa2 -17.982 kJ/mol of atoms; CoSeVa3-a -20.104 kJ/mol of atoms; CoSeVa3-b -20.755 kJ/mol of atoms; CoSeVa4 -17.847 kJ/mol of atoms; CoSeVa5 -20.944 kJ/mol of atoms and the average heats of formation of vacancies ∆H ̅^f (Va) are as follows: CoSeVa1 -79.432 kJ/mol Va; CoSeVa2 -65.837 kJ/mol Va; CoSeVa3-a -58.409 kJ/mol Va; CoSeVa3-b -64.700 kJ/mol Va; CoSeVa4 -22.979 kJ/mol Va; CoSeVa5 -31.537 kJ/mol Va.

Keywords

ab initio výpočty, teorie funkcionálu hustoty, program VASP, selen, SnSe2, CoSe, NiSe, vakance, tvorné teplo, ab initio calculations, density functional theory, VASP code, selenium, vacancy, heat of formation

Language used: Czech

Date on which the thesis was submitted / produced: 4. 1. 2023

Thesis defence

• Date of defence: 8. 2. 2023
• Supervisor: doc. Mgr. Jana Pavlů, Ph.D.
• Reader: Ing. Monika Všianská, Ph.D.

Masaryk University

Faculty of Science

Bachelor programme / field:
Chemistry / Chemistry