یہ عشق میں نہ سوچ، تُجھے کیا نہیں ملا
ہے کر لیا، تو خاک میں اپنی جبیں ملا
ہم راہ دیکھتے ہی رہے جس کی عمر بھر
آیا وہ شہر میں بھی تو ہم سے نہیں ملا
بچپن میں دل کی بستی میں رہتے تھے کتنے لوگ
دیکھا شباب میں تو فقط اک مکیں ملا
اگلے جہاں کے عہد پہ ہم کو دیا ہے ٹال
کم بخت ہم کو وہ تو بلا کا ذہیں ملا
کہتے رہے تھے یار جسے ہم تمام عمر
اک دن عدو کی بزم میں وہ نازنیں ملا
گر یاں دیا نہ تُو نے تو نہ لوں گا حشر میں
یارب اسے اگر ہے ملانا، یہیں ملا
Constructivism is the basis for thinking of a contextual approach, namely that knowledge is built not a set of facts, concepts, or rules that are ready to be remembered. Students must construct that knowledge and give meaning through real experience. Students need to be accustomed to solving problems, finding something useful for themselves, and struggling with ideas. The teacher will not be able to give all knowledge to students. Students must construct knowledge in their own minds. Knowledge is not static, but is constantly evolving and changing as students construct new experiences that force them to base themselves and modify previous knowledge. Learning must be packaged into the process of constructing knowledge rather than receiving knowledge. In the learning process, students build their own knowledge through active involvement in the learning and teaching process. Students become the center of activities, not teachers. Critical thinking is an attempt by someone to check the truth of information using the availability of evidence, logic, and awareness of bias. Critical thinking skills are the cognitive processes of students in analyzing systematically and specifically the problems faced, distinguishing these problems carefully and thoroughly, as well as identifying and reviewing information to plan problem solving strategies.
In this thesis, we present theoretical studies of antiperovskites ANCa3 (A=Ge, Sn, Pb), BCFe3 (B=Al, Zn, Ga), SnCD3 (D=Co and Fe) and MXY3 (M=Al, Ga, Ir, Mg, Pd, Pt, Rh; X=C, N; Y=Mn, Ni, Sc, Ti, Cr, Fe) as well as SbNCa3, BiNCa3, SbNSr3 and BiNSr3. The calculations are carried out with the full-potential linearized augmented plane waves plus local orbital (FPLAPW+lo) method within the framework of density functional theory (DFT) as well as Boltzmann’s theory. The exchange–correlation effects are treated by the local density approximation (LDA), generalized gradient approximation (GGA-PBEsol) and Engel and Vosko GGA (EV-GGA). Furthermore, the modified Becke and Johnson (mBJ) as well as improved mBJ potentials are used for the exact band gaps of the semiconductors. The relativistic effects in some of the compounds under study are explored by spin-orbit coupling. The consistency of the calculated results of the thermoelectric properties of SnCCo3 and SnCFe3 with the experimental results confirms the reliability of our theoretical calculations for the other investigated metallic antiperovskites, ANCa3 (A=Ge, Sn, Pb), BCFe3 (B=Al, Zn, Ga), SnCD3 (D=Co and Fe) and MXY3 (M=Al, Ga, Ir, Mg, Pd, Pt, Rh; X=C, N; Y=Mn, Ni, Sc, Ti, Cr, Fe). Our results for ANCa3 (A=Ge, Sn, Pb), BCFe3 (B=Al, Zn, Ga) and SnCD3 (D=Co, Fe) indicate that the thermopower of these materials can be enhanced by changing the chemical potential. The dimensionless figure of merit for the three nitrides approaches to 0.96 at room temperature, which predicts the usefulness of these materials in thermoelectric devices. Furthermore, the thermal conductivity of these compounds is minimum at room temperature for chemical potential of -0.25 eV to 0.25 eV, with maximum values of dimensionless figure of merit in this range. The striking feature of these studies is identifying a metallic compound, SnNCa3, with the highest value of Seebeck coefficient at room temperature out of all metals. Furthermore, electronic and thermoelectric properties of carbon and nitrogen based twenty metallic antiperovskites MXY3 (M=Al, Ga, Ir, Mg, Pd, Pt, Rh; X=C, N; Y=Mn, Ni, Sc, Ti, Cr, Fe) are investigated. We find high values of Seebeck coefficient and small values of electronic thermal conductivity for AlCTi3, AlNSc3, AlCNi3, AlNTi3, GaCCr3 and MgCNi3 between -0.25 and 0.25 eV chemical potential. These results show high dimensionless figure of merit in metallic materials and therefore, we predict these materials can be potential candidates for low temperature thermoelectric applications. Figure of merit for AlNTi3, GaCCr3, AlCNi3, AlNSc3, MgCNi3 and AlCTi3 materials reaches to 0.32, 0.25, 0.19, 0.19, 0.2 and 0.25 respectively, and hence are predicted to be low temperature thermoelectric materials. The structural, electronic and optical properties of antiperovskite semiconductors, SbNCa3, BiNCa3, SbNSr3 and BiNSr3 are also studied. The calculated lattice constants for these compounds are found consistent with the available experimentally measured values and other theoretical results. The band profiles show that all of these materials are direct band gap semiconductors with the band gap values of 1.1 eV, 1.09 eV, 0.92 eV and 0.81 eV for SbNCa3, BiNCa3, SbNSr3 and BiNSr3 respectively. The direct band gap nature reveals that they may be effective in optical devices and therefore the optical properties of these compounds like the real and imaginary parts of dielectric function, refractive index and absorption coefficient are calculated and discussed. Furthermore, the thermoelectric properties of these semiconductors are also calculated. Our results show high values of Seebeck coefficient for these materials between -0.25 eV and 0.25 eV chemical potential values.