Sains Malaysiana 39(2)(2010): 281–283

Ab Initio Calculations of Vibrational Frequencies in a Glassy State of Selenium

(Pengiraan Ab Initio bagi Frekuensi Getaran pada Selenium Berkeadaan Kaca)

Ahmad Nazrul Rosli*, Hasan Abu Kassim & Keshav N. Shrivastava

Jabatan Fizik, Fakulti Sains, Universiti Malaya

50603 Kuala Lumpur, Malaysia

Received: 19 May 2009 / Accepted: 29 July 2009

ABSTRACT

We used the density functional theory to calculate the vibrational frequencies of clusters of atoms. We obtained the bond distances and angles for which the energy of the Schršdinger equation is minimum. We found the bond distance between two Se atoms to be 232.1 pm when double zeta wave function was used. The frequency of oscillations was calculated to be 325.3 cm-1 but the intensity was zero because Se2 molecules were present in a very small number. When polarised double zeta wave function (DZP) was used, the bond length of Se2 was found to be 223.1 pm and the frequency is 367.4 cm-1. Similarly for other clusters of selenium, we calculated the frequencies and compared with the experimental data. The experimental Raman spectra give 250 cm-1 for a selenium glass. By comparing the experimental frequencies with those calculated we found that linear Se3 was present in the glass. This indicates the possibility of linear growth in the glass.

Keywords: Density functional theory; glass; raman spectra; selenium; vibrational frequencies

ABSTRAK

Kami menggunakan teori fungsi ketumpatan untuk membuat pengiraan bagi frekuensi getaran bagi kelompok atom. Apabila tenaga persamaan Schršdinger diminimumkan, kami dapat mengukur panjang ikatan dan sudut bagi atom-atom. Panjang ikatan bagi dua atom Se adalah 232.1 pm dengan menggunakan fungsi ikatan zeta berganda. Frekuensinya adalah 325.3 cm-1 tetapi keamatannya adalah sifar disebabkan kehadiran sangat sedikit molekul Se2. Apabila fungsi gelombang zeta berganda berkutub digunakan, panjang ikatan adalah 223.1 pm dan frekuensinya adalah 367.4 cm-1. Sama juga bagi kelompok selenium yang lain, kami mendapatkan frekuensi gelombang untuk dibandingkan dengan data eksperimen. Data eksperimen bagi spektrum Raman menunjukkan nilai 250 cm-1 bagi kaca selenium. Perbandingan dengan data eksperimen menunjukkan Se3 linear wujud dalam kaca. Ini menunjukkan kemungkinan pertumbuhan secara linear dalam kaca.

Kata kunci: Frekuensi getaran; kaca; spektrum Raman; selenium; teori fungsi ketumpatan

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*Corresponding author; email: anazrul84@yahoo.com