Photograph of multicoloured tiles (black, white, blue, green, and yellow) arranged with two-fold rotational symmetry and a pair of orthogonal mirror orientations. Without colouration, the pattern would have six-fold rotational symmetry and six mirror orientations.
Tiling in the Palace of the Lions (p2mm symmetry). #TilesOnTuesday #Tiling #Alhambra #Granada #Andalucia #Architecture #Symmetry #Photography
Photograph of multicoloured tiles (black, white, blue, green, and yellow) arranged with two-fold rotational symmetry and a pair of orthogonal mirror orientations. Without colouration, the pattern would have six-fold rotational symmetry and six mirror orientations.
Tiling in the Palace of the Lions (p2mm symmetry). #TilesOnTuesday #Tiling #Alhambra #Granada #Andalucia #Architecture #Symmetry #Photography
An effigy of a man in sumptuous colthing, staring contemplatively at a skull that he holds in his left hand.
Effigy in Granada Cathedral. #MementoMoriMonday #MonumentMonday #Skull #Granada #Andalucia #Photography
An effigy of a man in sumptuous colthing, staring contemplatively at a skull that he holds in his left hand.
Effigy in Granada Cathedral. #MementoMoriMonday #MonumentMonday #Skull #Granada #Andalucia #Photography
Photograph of a modern stained glass window in the shape of a tall arch, its vibrant colours standing out boldly against entirely black surroundings. The colours range from yellow and red at the base, rising through green and then blue, culminating in a mixture of hues toward the apex. The lower portion contains billowing shapes evocative of a seashore, while the middle section contains myriad seabirds in whirling flight, ascending to a more abstract realm above.
The Illumination Window, Durham Cathedral. Mel Howse (2019) in Memory of Sara Pilkington. #StainedGlassSunday #Durham #Cathedral #StCuthbert #Seascape #Birds #Photography
Photograph of a modern stained glass window in the shape of a tall arch, its vibrant colours standing out boldly against entirely black surroundings. The colours range from yellow and red at the base, rising through green and then blue, culminating in a mixture of hues toward the apex. The lower portion contains billowing shapes evocative of a seashore, while the middle section contains myriad seabirds in whirling flight, ascending to a more abstract realm above.
The Illumination Window, Durham Cathedral. Mel Howse (2019) in Memory of Sara Pilkington. #StainedGlassSunday #Durham #Cathedral #StCuthbert #Seascape #Birds #Photography
Close-up photograph of a small plant with a single main stem and several sprays of tiny white flowers. The plant (which is maybe cow parsley) is in sharp focus, while the background (rocks and still water) is in soft focus.
On the Banks of Loch Lomond. #FlowersOnFriday #Flowers #LochLomond #Trossachs #Scotland #MacroPhotography #Photography
Close-up photograph of a small plant with a single main stem and several sprays of tiny white flowers. The plant (which is maybe cow parsley) is in sharp focus, while the background (rocks and still water) is in soft focus.
On the Banks of Loch Lomond. #FlowersOnFriday #Flowers #LochLomond #Trossachs #Scotland #MacroPhotography #Photography
Just published today, we are delighted to share our paper entitled “Chemical Softness as a Predictor for Reactivity at Metal Surfaces” #ChemSky #CompChemSky
Photograph of sandy-coloured tiles arranged in a six-fold rotationally symmetric pattern, devoid of mirror symmetry. The repeating motif comprises a six-pointed star, surrounded by Z-shaped and roughly L-shaped tiles. The finish is matt, and the colouration variable. The eye is mostly drawn to the black lines between the tiles, rather than to the tiles themselves.
Tiling in the Palace of the Lions (p6 symmetry). #TilesOnTuesday #Tiling #Alhambra #Granada #Andalucia #Architecture #Symmetry #Photography
Nevertheless, we believe that the concept of chemical softness may yet find a role as an adjunct to other simple measures, each of which may capture different aspects of surface reactivity. More work, as ever, remains to be done.
We confirm that there is a general trend for surfaces with the softest top-layer atoms to bind CO most strongly, albeit with considerable scatter in the data. Overall, analysis of chemical softness shows some promise in predicting binding energy but lacks the predictive power we hoped for.
Although we focus here on binding energy, it is well-known that barriers to chemical reactions (dissociation, for example) tend to correlate strongly with the strength of binding to the surface on which they occur. A result obtained for binding energies will thus have implications for reactivity.
In this new paper, we extend our method to a range of surfaces (three different facets each for copper, silver, gold, rhodium, palladium, and platinum) and examine how the binding energy for carbon monoxide (CO) corelates with the chemical softness of the uppermost metal atoms.
We have previously proposed a practical approach to calculating chemical softness at metal surfaces, applying it to understand the way that adsorption on a platinum surface can change the chemistry of so-called aromatic molecules.
Annoyingly, however, this workaround compromises the calculation of the chemical softness in ways that depend upon the precise model we have chosen for the surface and the vacuum region above it. Some way to standardise how we model the surface and interpret the softness is clearly needed.
But since we need to add or subtract electrons to calculate softness, we are faced with systems in which non-zero electric charge is periodically replicated in three dimensions – a situation that strictly implies infinite energy. To avoid this, the code has to incorporate a clever workaround.
Modern computer codes typically exploit the fact that a metal’s crystalline structure repeats itself in the two dimensions parallel to the surface. It is also, however, computationally efficient to include a fake repetition in the third dimension too. This presents no problem for neutral surfaces.
In essence, chemical softness is a measure of how much (and where) electron density accumulates (or is diminished) when electrons are added to (or subtracted from) a given system. When dealing with surfaces, however, an ambiguity is introduced due to the way we handle extended systems.
Several such models of reactivity have been proposed and explored, with varying degrees of success, but the measure that we've been looking at – the chemical softness – has already shown its worth in studies by others of purely molecular systems; the challenge lies in applying it to metal surfaces.
What we need is a simplified reactivity model – based on existing detailed calculations – that can be applied rapidly across a wide range of systems, giving a ballpark estimate of which are likely to be highly reactive and which will be duds. We can then focus our effort on the most promising cases.
Although very successful, this approach can only go so far. There are so many possible molecules to consider, on so many differently prepared surfaces, that it is simply not possible to carry out detailed studies on every conceivable combination of interest.
Over the last thirty or more years, computational surface chemists have applied sophisticated quantum calculations to problems in heterogeneous catalysis – where interaction with metal surfaces causes reactions that would otherwise be slow to become faster and more practically viable.
Just published today, we are delighted to share our paper entitled “Chemical Softness as a Predictor for Reactivity at Metal Surfaces” #ChemSky #CompChemSky
Photograph of sandy-coloured tiles arranged in a six-fold rotationally symmetric pattern, devoid of mirror symmetry. The repeating motif comprises a six-pointed star, surrounded by Z-shaped and roughly L-shaped tiles. The finish is matt, and the colouration variable. The eye is mostly drawn to the black lines between the tiles, rather than to the tiles themselves.
Tiling in the Palace of the Lions (p6 symmetry). #TilesOnTuesday #Tiling #Alhambra #Granada #Andalucia #Architecture #Symmetry #Photography
Photograph of a wall-mounted oval plaque bearing a coat of arms, illuminated by varicoloured light streaming from a nearby stained glass window. The arms comprise four white lions in rampant posture positioned around a gold cross on a blue background. The cross has decorativ ends in the form of fleurs-de-lis. The whole is surrounded by scrollwork, surmounted by the head and hands of a crowned figure.
Arms of the Diocese of Durham, in Durham Cathedral. Azure a cross fleury or between four lions rampant argent. #StainedGlassSunday #Durham #Cathedral #Heraldry #CoatOfArms #Photography
Photograph of a wall-mounted oval plaque bearing a coat of arms, illuminated by varicoloured light streaming from a nearby stained glass window. The arms comprise four white lions in rampant posture positioned around a gold cross on a blue background. The cross has decorativ ends in the form of fleurs-de-lis. The whole is surrounded by scrollwork, surmounted by the head and hands of a crowned figure.
Arms of the Diocese of Durham, in Durham Cathedral. Azure a cross fleury or between four lions rampant argent. #StainedGlassSunday #Durham #Cathedral #Heraldry #CoatOfArms #Photography
Black and white photograph of a crenellated round tower, almost in silhouette against the sky. In the upper third of the frame, that sky is clear, but the lower two thirds are clouded; bright sunlight illuminates the boundary. The tower itself is rather squat, designed for defence against artillery, and to provide an artillery firing platform at its upper level.
Artillery Tower, Threave Castle. #CastleSaturday #Castles #ThreaveCastle #DumfriesAndGalloway #Medieval #LateMedieval #Architecture #Monochrome #BlackAndWhite #Photography
Black and white photograph of a crenellated round tower, almost in silhouette against the sky. In the upper third of the frame, that sky is clear, but the lower two thirds are clouded; bright sunlight illuminates the boundary. The tower itself is rather squat, designed for defence against artillery, and to provide an artillery firing platform at its upper level.
Artillery Tower, Threave Castle. #CastleSaturday #Castles #ThreaveCastle #DumfriesAndGalloway #Medieval #LateMedieval #Architecture #Monochrome #BlackAndWhite #Photography
Black and white photograph looking uphill through a scatter of tombstones and assorted funerary monuments. A stunted obelisk dominates the left foreground, while a dark shadow encroaches from the right of frame. The sky is largely clear with wispy clouds.
Glasgow Necropolis. #TombTuesday #Gravestones #Cemeteries #Necropolis #Glasgow #BlackAndWhite #Monochrome #Photography