An Entropic Approach to Classical Density Functional Theory

The classical Density Functional Theory (DFT) is introduced as an application of entropic inference for inhomogeneous fluids in thermal equilibrium. It is shown that entropic inference reproduces the variational principle of DFT when information about the expected density of particles is imposed. This process introduces a family of trial density-parametrized probability distributions and, consequently, a trial entropy from which the preferred one is found using the method of Maximum Entropy (MaxEnt). As an application, the DFT model for slowly varying density is provided, and its approximation scheme is discussed.

Using DFT to Calculate the Parameters of the Crystal Field in Mn2+ Doped Hydroxyapatite Crystals

Crystal field parameters for two nonequivalent positions Ca (I) and Ca (II) for hydroxyapatite (HAp) crystals from the density functional theory (DFT) are calculated. Calculations are compared with the experimental electron paramagnetic resonance (EPR) spectra (registered at two microwave frequencies) for the synthesized Mn-HAp powders Ca9.995Mn0.005(PO4)6(OH)2. It is found that in the investigated species, the manganese is redistributed between both calcium sites with prevalence in Ca (I). Agreement between the calculated and experimental data proves that crystal field parameters in HAp can be calculated in the classical DFT model using the distributed electron density.

Principles of Dopamine Binding to Carbon Surfaces

Fast Scan Cyclic Voltammetry (FSCV) combined with carbon electrodes is considered as the gold standard method for real-time detection of oxidizable neurotransmitters. The bioinert nature, rapid electron transfer kinetics and long-term stability make carbon an attractive material for probing brain electrochemistry. Herein, we first demonstrate a rapid fabrication process of carbonized nanopipettes and subsequently perform experimental measurements and theoretical simulations to study mechanisms of dopamine binding on carbonized surfaces. To explain the kinetics of dopamine oxidation on carbonized electrodes we adapted the electron-proton transfer model originally developed by Compton and found that the electron-proton transfer model best explains the experimental observations. We further investigated the electron-proton transfer theory by constructing a Density Function Theory (DFT) for visualization of dopamine binding to graphite-like surfaces consisting of heteroatoms. For graphite surfaces that are capped with hydrogen alone, we found that dopamine is oxidized, whereas, on graphite surfaces doped with heteroatoms such as nitrogen and oxygen, we found deprotonation of dopamine along with oxidation thus validating our experimental and theoretical data. These observations provide mechanistic insights into multistep electron transfer during dopamine oxidation on graphite surfaces.Graphical abstractA: Pictorial view of the experimental setup of carbonized electrodes. The application of waveform causes the oxidation of dopamine. B. Background subtracted voltammogram of dopamine, wherein the waveform applied is -0.4V to 1.3V and cycled back at -0.4V at 200 V s-1 at 10 Hz. C: A hotspot showing the oxidation and reduction of dopamine, wherein two distinct redox spots can be seen. The first redox spot can be seen at 0.0V and the second one at 0.5V. Thus showing a multistep electron transfer for dopamine. D: A DFT model for dopamine’s interaction with graphite surfaces doped with nitrogen atoms. Oxidation of oxygen (red) can be seen with loss of protons.

APLIKASI SISTEM AQUAPONIK DENGAN HIDROPONIK DFT PADA BUDIDAYA TANAMAN SELADA (LACTUCA SATIVA L.)

Aquaponik merupakan salah satu cara budidaya tanaman dengan hidroponik bersamaan dengan budidaya ikan, dimana air berputar terus tanpa berhenti. Pada sistem aquaponik tidak memerlukan nutrisi AB mix untuk memberikan unsur hara pada tanaman, tetapi unsur hara diperoleh dari air kolam ikan yang mengandung nutrisi, yang berasal dari ikan. Selada (Lactuca sativa L.) yang ditanam secara hidroponik merupakan sayuran yang digemari karena harganya tinggi dan sehat untuk dikonsumsi. Tujuan dari penelitian ini adalah untuk mengetahui adanya tidaknya perbedaan hasil budidaya tanaman selada secara aquaponik menggunakan tiga model hidroponik DFT. Metode yang digunakan adalah pengukuran lapangan, yang meliputi tinggi tanaman, jumlah daun, dan berat tanaman selada, serta analisis data hasil pengukuran. Selain itu juga dilakukan pengukuran suhu, pH dan konsentrasi air kolam, serta kandungan amonia pada air kolam. Hasil pengukuran lapangan dengan hidroponik DFT model meja, model piramida, dan model anak tangga dianalisis untuk mengetahui apakah terdapat perbedaan menggunakan Anava (Analisis Varians) satu jalan pada taraf signifikansi 5%. Berdasarkan Anava diketahui bahwa terdapat perbedaan hasil pengukuran tanaman selada dengan menggunakan ketiga model hidroponik DFT, dan yang berpengaruh paling baik adalah model piramida, dengan hasil rata-rata 21,8 cm untuk tinggi tanaman, rata-rata 8,4 helai untuk jumlah daun, dan rata-rata 75,3 g untuk berat tanaman.

Pengaruh Aplikasi Tiga Model Hidroponik DFT Terhadap Tanaman Pakcoy (Brassica rapa L.)

Deep Flow Technique (DFT) merupakan salah satu sistem hidroponik dimana akar tanaman diletakkan dalam lapisan air dengan ketinggian 3 – 4 cm. Air tersebut tersirkulasi karena adanya dorongan dari pompa dan mengandung nutrisi sesuai kebutuhan tanaman. Beberapa model hidroponik DFT yang sudah dikembangkan diantaranya adalah model meja, model piramida, dan model anak tangga, dan ketiga model tersebut digunakan dalam penelitian ini. Tujuan dari penelitian ini adalah untuk mengetahui ada tidaknya perbedaan terhadap rata-rata tinggi tanaman, jumlah daun, dan berat tanaman pakcoy pada ketiga model hidroponik DFT tersebut. Analisis yang digunakan adalah Anava (Analisis Varians) one way karena hanya ada satu variabel independen pada taraf signifikansi 5%. Berdasarkan hasil penelitian menunjukkan bahwa terdapat perbedaan rata-rata tinggi tanaman, jumlah daun, dan berat tanaman pakcoy dengan menggunakan hidroponik DFT model meja, model piramida, dan model anak tangga. Hidroponik DFT model piramida merupakan model yang menghasilkan tinggi tanaman paling baik, jumlah daun paling banyak, dan berat tanaman paling besar apabila dibandingkan dengan hidroponik DFT model meja dan model anak tangga, dengan hasil rata-rata tinggi tanaman 18.4 cm, rata-rata jumlah daun 10.8 helai, dan rata-rata berat tanaman 111.8 g.

Carbon monoxide formation from trimethylamine-boranecarboxylate: DFT studies of SNi and chelotropic mechanisms

According to a DFT model, CO is formed from trimethylamine boranecarboxylate, a carbon monoxide releasing molecular pro-drug (CORM), via initial SNi subsitution followed by chelotropic fragmentation of the resulting cyclic carboxyborane anion.

Disorder in La1−x Ba1+x GaO4−x/2 ionic conductor: resolving the pair distribution function through insight from first-principles modeling

Ionic conduction in dry LaBaGaO4 occurs through the vacant oxygen sites formed by the substitution of Ba for La. The resulting La1−x Ba1+x GaO4−x/2 solid solution shows significant disorder characteristics. The local structure of compositions x = 0, 0.20 and 0.30 was studied using the pair distribution function (PDF). Unfortunately, increasing peak overlap and the number of independent structural parameters make PDF modeling challenging when dealing with low-symmetry phases. To overcome this problem, density functional theory (DFT) was employed to create different structural models, each one with a different relative position for the substitutional Ba ion with respect to the oxygen vacancy. The atomic distributions generated by DFT were used as a starting point to refine experimental PDF data. All models result in the formation of Ga2O7 dimers, with their major axis oriented along the c axis. At the local scale, the most stable DFT model also provides the best fit of the PDF. This accounts for the dopant as first and second neighbors of the vacancy and of the O bridge in the dimer, suggesting that substitutional barium ions act as pinning centers for oxygen vacancies. Above 6 Å the average orthorhombic structure fits the PDF better than the DFT models, thus indicating that Ga2O7 dimers are not correlated with each other to form extended ordered structures. The combination of DFT simulations and X-ray diffraction/PDF refinements was used successfully to model the local atomic structure in La1−x Ba1+x GaO4−x/2, thus suggesting that this approach could be positively applied in general to disordered systems.